Last night, disturbing cell-phone video surfaced of South Carolina police officer Michael Slager shooting Walter Scott, an unarmed black man, in the back and killing him as he fled from an altercation they’d had. Now many are asking why Slager then proceeded to handcuff Scott. Science of Us answered that question last August, after another incident involving a police shooting.

One of the (many) horrible details about the video of the police-shooting death of Kajieme Powell — and one I didn’t mention in my article about the incident — is the fact that the police handcuff Powell after shooting him multiple times. In the video of the incident (again, don’t watch if squeamish), you can hear the man who is filming comment on this. It’s an understandable question: Why would the police do this? It comes across as a desecration.

In short, because they’re trained to. Below are some guidelines from the August edition of The Police Chief, a law-enforcement publication, on what cops should do in situations like this (hat tip to Joshua Holland for pointing this out to me). They’re based at least in part on a Justice Department research project called Preventing Violence Against Law Enforcement and Ensuring Officer Resilience and Survivability, or VALOR:

Lesson 8: Handcuff all downed suspects. Some officers might feel that it is not nice to handcuff suspects that have been shot, and others might believe that it is unnecessary to cuff all suspects because some are “obviously” dead. Counted among the suspects shot during incidents that officers reported during the VALOR interviews were some who appeared to be dead—for example, from multiple rifle rounds to the head—but who were still alive. As noted in the introduction, some human beings have a remarkable capacity to survive gunshot wounds. Fortunately, none of the thoughtdead offenders managed to injure any officers interviewed, but the fact that they were still alive meant that they maintained the capacity to do so. The capacity of downed suspects is hindered substantially when they are cuffed. No matter how severely injured they might be, therefore, all downed suspects should be handcuffed.

As Brian Beutler pointed out in The New Republic, there are many aspects of police protocol that come across as cruel or strange to civilians. This certainly fits in that category.