Collection of a Crime Scene Using Laser Scanners by Det. Mike Anderson

Collection of a crime sceneDetective Michael S. Anderson

Unified Police of Greater Salt Lake County

Office 385-468-9821

Cell 801-884-9398

Collection of a crime scene

• What are the advantages of scanners over other measuring methods used. Pros and Cons for each.

• How accurate is the data captured in laser scanning

• Should we scan or shouldn’t we ( our environmental issues )

• Scene set up things to consider

• When should we introduce the scanner to a scene

• What admissibility does laser scan data have in our court systems

• Closing some common mistakes made in 3D laser scanning


• What are the other measuring options?

• Total Station

• Photogrammetry

• Tape Measure


• Can we do an effective measuring job with a total station?

• The answer is we absolutely can, and they do a great job.

• Can we measure effectively with Photogrammetry?

• Again yes we can. If your not use to modeling with pictures it can be tricky, but yes it is a very good an effective way to measure many things and that includes a crime scene.

• How about a good old fashioned tape measure.

• Well yes you can..


• Although a total station is a great and effective tool it is extremely time consuming on scene

• Our average on scene time running two total stations surveying the average two story home could take us up to 5 to 7 hours of survey time

• This also requires for us approximately 6 officers or workers to accomplish the survey.

• We are redundant!!!!!!

• Total station is reasonable in cost for the work it does


• Photogrammetry or Photomodeling??

• This is a very inexpensive way to create to scale a drawing and it is extremely effective for the cost.

• You will need a decent camera, modeling software and some markers for identification as well as a few incidentals like tape measures, tri-pods etc.

• The accuracy of this method relies heavily on the user itself.


• How about the average in home tape measure?

• Yes even with this and the proper measuring techniques you can measure a crime scene to scale.

• This is still common place in law enforcement.

• However what time is involved here?

• Is there scribing and accuracy issues with this method as well?

• If mistakes are made how do you correct them?


• Now the new kid on the block.

• 3D laser scanning

• At least to most Law Enforcement agencies this stuff is brand new.

• Even though scan capability is not new.

• So why scanners over the other methods?

• The cost is certainly higher than any of the other previously mentioned methods, and those methods certainly work.


• The first and primary reason is the overall scene preservation which comes from scanning.


• With scan data if the scanner sees it you have measured it. Even if you don’t know at that time you needed to measure a certain item.

• This really takes a lot of evidence guess work away for an investigator, and from the investigation as a whole.

• For example you have a crime scene today, and as part of the processing of the crime scene the investigators or crime scene personnel will placard or ID in some way a particular piece of evidence.


• But what happens if you aren't aware of something as being evidence until after you have cleared the scene? And you didn’t measure that item in prior to clearing the scene.

• Using a total station or tape measure there would be very little that could be done from a surveying stand point to help you.

• Maybe with Photogrammetry you could try and add it in at a later time, but that takes experience and in many cases an extensive amount of work to create, and that’s if you have everything you need already to conduct that analysis.


• But the advantage with laser scanning is that if scanned it is there no matter when it was discovered to be of evidentiary value .

• Think of scanning in this way, if your eye can see it then the scanner sees it also, and it appears in much the same way, to many as an image.

• And it is then preserved for a lifetime


• And since it is recorded and preserved for a lifetime.

• You can place anyone back in that scene to scale in 3D at anytime it is needed.

• To sum it up 3D scanning is a game changer for us and how we document and preserve any scene rather a crime scene or crash scene.


• Real world case example

• OIS in the western part of Salt Lake County

• Officer is advanced on by an edged weapon assailant

• The assailant is actively cutting his own throat prior to the shooting taking place

• As the officer is advanced on the assailant gets within 6 feet of the officer before the final rounds fired from the officers weapon defeat the assailant


• Due to the proximity of the assailant to the officer at the time. The officer was firing downward as the assailant fell and approached the officers location.

• It was later determined from the investigation that there were two bullet strikes in a downward attitude in the roadway surface from the officers weapon

• However this wasn’t known or discovered until after the scene had been scanned and all evidence had been collected, and the scene was released. In fact this was discovered approximately 48 hours after the event was cleared.


• The process then became to try and identify these bullet strikes in the roadway and include them in the after action scale scene drawing.

• Suspect view looking towards the officer location

• The white paint is blood drops from the suspect cutting his throat prior to the shooting.


• Officers view looking back towards the originating location of the advancing suspect.


• Bullet strikes in the roadway not placard, identified or marked the night of the shooting.


• The end result 2D topical after action scene drawing


• So how accurate are scanners?

• Well its fairly standard that scan data has an accuracy of approximately + or -2mm within 25m, or 0.08 inch within 86 feet.


• When should we scan and when cant we?

• Currently we scan in every situation.

• So long as the mirror’s and the scanner stays dry. Scan!


• Snow is a major problem for us. However even with snow scanning is not an issue.


• Snow scans cont.


• Snow cont.


• Snow cont.


• Rain?

• Cover interference


• Heat & cold concerns

• Certainly heat and cold weather do pose an issue

• Excessively hot and or cold days do have an effect on the performance of the scanner. Or even being able to scan.

Collection of a crime scene and documentation

• When the FARO is exposed to temperatures ranging from approximately 10 to 15 degrees on the cold end to 110 degrees on the hot side. The FARO scanner will tend to shut down and will not perform until it recognizes a safe temperature.

• When scanning in colder weather however if you keep scanning consistently the scanner tends to do better, and not stop on you since the internal heat from use keeps it going.

• However if you over heat during scanning the scanner will need to be placed in a cool place and allowed to cool prior to proceeding with the scan job.

Collection of a crime scene and documentation• Scene set up things to consider

• What is your scene?

• How large is your scene?

• Will you be required to scan in several locations to complete the job you want?

• What interference will you have?


• What is the end result you are desiring

• Always try to set the scanner and the spheres in a manner that you maximize your scanner capability.

• By doing this you can get the most scan data for the time you spend on a scene scanning.

• Its always a good idea when possible to have assistance.

• This allows you to keep scanning while assistance that you have are setting spheres and reference points up ahead of you.

• By doing it this way you can be more efficient and faster than doing it alone.

Collection of a crime scene• What is your scene?

• Indoor scenes can be more difficult to scan than most outdoor scenes

• There is always going to be much more to consider indoors.

• Such as how many changes occur to wall lines, furniture, appliances, door ways, rooms and any other introduced items to an interior scene.

• The setting up of spheres, and reference markers can be more complex, and may need more thought as you set and scan or survey.


• Outdoor scenes tend to be more wide spread and less to consider than an interior scene. Outdoor scenes tend to flow smoother.

• The setting up of spheres and reference points allow you in many cases to get more scans accomplished with the same reference in place.

• Certainly outdoor scenes pose their own challenges, but for the most part they can be a little simpler to deal with.

• How about transition scanning, or surveying such as going from the outdoor scene to an indoor scene or visa versa.

• This situation is very simple to deal with so long as you have the correct amount and same common points for the transition scans, or survey, then no issue.


• Introducing a scanner or investigator to a scene?

• When should we introduce not only the scanner, or total station but ourselves into the scene.

• It really depends on how your agency is set up to processes crime scenes.

• If you are the scene processor and the one who will scan, or measure then your entrance is irrelevant.

• Limiting the exposure to the scene from outside influences, such as unwanted or un needed personnel, to animals is always the best policy to follow.


• Many crime scene investigators prefer to complete overall scene photographs prior to scanning, and this may be a good approach. But it is important that scanning be completed as soon as practical after those initial photos are taken. Waiting too long can lead to discrepancies between the two sets of documentation, and that can raise questions and compromise for the investigation.

• Our practice follows this rule, however prior to our presence the scene is also placard and photo'd prior to the scans being done.

• You also need to keep in mind the need to be able to do additional scans in areas you have already scanned. This is accomplished by leaving reference points in place such as paper targets or spheres if you can afford to leave them in place


• The next consideration in all of this is when to remove the body, if you have a body present.

• It has become strongly recommended that all scans or measurements of any type be completed before the removal of any evidentiary item including the body.


• Like any other piece of evidence that is admitted in court, 3D Scanning is going to face the same kinds of scrutiny as any other piece of measurement equipment whether it be a total station, GPS, photogrammetry...etc.

• It doesn’t matter what creates the data be prepared to defend the data.

• This includes certified documentation of the calibration of your equipment no matter what the equipment may be.

• Of course, the court systems around the world are all different and admissibility is often subjective based on past experience, the judge and to some extent, the lawyers who are involved in the case. However, in general terms admissibility of 3D Scanners and their resultant data needs to fall under some generally accepted rules. On that note, here are some things to consider in no particular order:


1. Training and Experience of User - With the growing use of 3D Scanners, there are going to be more and more users coming on board that need training on the use of the equipment and an understanding of the technology which drives it. There are two sides to this equation. One is for the operation of the 3D Scanner and the other is the post analysis with specialized software. It is imperative that 3D Scanners are used as intended and users need to be aware of the pitfalls, errors and accuracies of any particular measurement.


• 2. Calibration of Equipment - Just like any piece of equipment. Regular maintenance is required and is often based on the manufacturer's recommended maintenance plan. This often gets people into trouble! (I could tell you stories of how many people I know got off on a speeding ticket because when they requested the maintenance and calibration log of the radar gun, it was never recently done).


• 3. Accuracy of Equipment and Error Rates - This is perhaps one of the most complex and least understood areas for any piece of equipment . There are many people who are excellent users of the equipment, but they know little of what to do with the data. When asked, "what is your maximum error?" you usually get a blank stare. Taking hand measurements or some kind of reference measurement to ensure you can estimate the accuracy and error of the object. 3D Scanning is especially tricky because of the amount of "noise" that can become apparent in any particular scan. Most people don't realize how much cleaning, filtering and manual tweaking is required to get a decent looking scan. Let's face it. The accuracy of an instrument and the accuracy of the measurement can be two very different things. Reflectance plays a big part here without having to worry about busy streets where you have a lot of "ghosting" from vehicles and people walking by. The key here is to have a comparative reference measurement and do not overstate the accuracy!

Collection of a crime scene• Failing to Create a Scan Plan

The early stages of a crime scene investigation can be hectic. Questions need to be answered as quickly as possible. Upon arrival, for example, a crime scene investigator might face queries such as: What’s the victim’s identity? Is there a weapon present? What is the serial number of the gun? How many shots were fired? The answers may be revealed by searching the scene, but first the scene must be thoroughly documented. However, before proceeding with laser scanning, a few minutes should be set aside to create a “scan plan.” A scan plan is a quick sketch of the scene layout that is prepared after the initial scene walkthrough but before documentation starts. Laying out a quick plan on paper helps determine the best setup locations for the scanner and targets so that the scene can be thoroughly documented in as few steps as possible. The plan also creates a written record of your activities at the scene.


• Showing Up with Uncharged BatteriesPreparedness is key. Showing up at a scene with dead or partially charged batteries will lead to embarrassing scene-processing delays. Although some scanners can operate on power plugs, there is no excuse for not being prepared and ready to go with fully charged batteries. Lithium-ion batteries can remain on the charger without harm during scanner downtime. So immediately upon returning from an assignment, place any dead batteries back onto the charger. Also, rotate batteries regularly so you can be sure that, when the call comes, you will be ready to get straight to work.


• Not Utilizing NIST Traceable Interim Validation ToolsThe National Forensic Science Technology Center now recommends that crime scene measurements have National Institute of Standards and Technology (NIST) traceability. According the center’s 2013 guidelines, measurements should be accurate to within 0.25 inch and “the accuracy of all measuring devices should be ensured by comparison to a measure of certified accuracy, such as a NIST traceable ruler.” Additionally, a criterion for federal court admissibility of scientific evidence under the DaubertStandard requires the establishment and maintenance of operational guidelines and protocols for conducting analytical testing, monitoring quality assurance and controls, periodic calibration checks and validations. When evaluating scanner performance specifications, look for technology and manufacturers that provides verifiable accuracy. Otherwise, your scan data evidence and exhibits may not hold up in court.


• Not Repeating Scans After New Evidence is DiscoveredOnce the scene is photographed and scanned, the next step is scene processing. During the processing, items are moved and new evidence may be revealed. Don’t forget to re-scan the areas where new evidence is discovered. For example, consider that a decedent is removed from the scene and a weapon is discovered under the body. If the area is re-scanned, before-and-after views can be layered into the point cloud and toggled on and off from view using 3D point cloud processing software.

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• Not Making Redundant Copies of DataBefore departing the crime scene, always copy your data onto an authorized flash drive. Redundant copies of data are good policy and protect the investigation against accidental loss. However, remember that scan data from a crime scene is evidence, and each copy must be properly secured and tracked.

• Whether the measurement tool is a traditional tape or a high-tech laser scanner, maintaining scene integrity and delivering incontrovertible data depends on circumspection and adherence to procedures and protocols. Avoid these six critical laser scanning mistakes, and you can be confident that your work will stay on track.

The End

Presentations & Public Speaking

Collection of a Crime Scene Using Laser Scanners by Det. Mike Anderson