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Five tips for successful forensic evidence collection at a mass crime scene

Pay attention to both the technical and the human aspects of the effort


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Large-scale crime scenes are a special challenge, and not solely because of the immensity of the task. Processing these sites often requires bringing in extra personnel for evidence handling, site security and support.

1. Control the scene

Your first challenge will be in securing the scene itself. Large-scale crime scenes tend to be outdoors, and will draw spectators, thrill-seekers, souvenir hunters and people who just like to disrupt police operations.

In this Oct. 4, 2017, file photo, agents from the FBI process evidence at the scene of a mass shooting in Las Vegas. (AP Photo/Gregory Bull, File)
In this Oct. 4, 2017, file photo, agents from the FBI process evidence at the scene of a mass shooting in Las Vegas. (AP Photo/Gregory Bull, File)

Uniformed law enforcement officers with proper training, equipment, communications and authority are the best choices for sentries, but they may be in short supply. You may be able to supplement the police with non-sworn personnel. Using uniformed people, even if they’re not law enforcement, helps with identification and public interaction. Non-sworn security personnel will always need to be backed up with law enforcement officers, but the non-sworn folks can serve as a force multiplier.

Brief everyone on the applicable laws concerning securing of crime scenes, and the limits of their authority. Don’t compromise an officer by assigning him to enforce rules for which there is no lawful foundation.

2. Grid the area

Before any evidence is marked or gathered, set up a grid to map the crime scene and document where everything came from. There are high-tech laser systems to do this, but some surveyor’s stakes and string work almost as well. The simplest systems use letters to identify marks on one axis and numbers for the other. Ideally, the grid lines should be aligned with cardinal points of the compass. This will help in plotting the grid on a map.

Every item of evidence should be identified as coming from a specific grid square, and possibly even a coordinate within that grid square, depending on the situation.

3. Photograph or scan in place

Every item of evidence should be photographed in place before anyone touches it. You will need some sort of system to associate each photo with a grid square, so the photos can be used to reconstruct the scene later. Digital photos and videos taken at the scene should be collected before the photographer leaves the scene. The images can be downloaded from cameras, but it may be faster to have memory cards available to swap out at the collection point.

There are 3D laser scanners available that can document every visible feature over a wide area, with extreme precision and detail. Highway patrols and big-city crime labs are more likely to have these. These systems are expensive, but you may be able to borrow one from another agency for a unique, large-scale crime scene. One way to make the request more palatable for the agency owning the gear is to offer to pay the expenses of the operators for the time they require on your site. The operators themselves may be eager to participate in a large-scale operation for the experience it will provide to them.

4. Use the metadata

When there are crowdsourced videos and photos of an incident – and there often are – gathering and indexing them can be a nightmare. You have to first find them, then determine whether the photo or video shows what it purports to show, and when and where it was captured.

Social media can be of help in gathering digital evidence. By putting out a call for assistance, people with relevant information can upload their files to shared resources like Dropbox and OneDrive.

When a review of the files show they contain relevant information, the metadata embedded in most smartphone media files can tell you the precise time and date the file was recorded, as well as the geographic coordinates where it was taken. By mapping these files, you may be able to get perspectives on the scene that wouldn’t have otherwise been available.

5. Support the troops

Working a crime scene, especially if the weather is not ideal, is a taxing, tedious job. Basic needs like portable toilets, rest and rehab areas, and access to water are the most basic requirements. If you can make food available on site, people will not need to leave for meal breaks, and can get what they need when they need it.

After the sniper attack from the Mandalay Bay Hotel in Las Vegas in 2017, volunteers from the local chapter of the Fraternal Order of Police, many of them retired cops, staffed a field kitchen 24/7 for weeks, supporting workers at the crime scene. They were supplemented by church and other civic groups. Food was supplied by local businesses. There was so much food offered that they had to work out a delivery schedule, so that none of it would go to waste.

You also need to keep your crime scene people in the loop. Schedule regular briefings for everyone, so as to limit the effect of rumors and keep everyone on the same page. Unless there is a specific reason not to release information, make sure everyone is informed as much as possible. This limits misunderstandings and makes people feel like they are a valued part of the effort.

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