I have a difficult time believing it isn’t part of training, either officially or unofficially.
An anecdote: when I was growing up my father was friends with a now very well known detective in our area. They would talk about some of the training he would attend where the focus was literally how to force a confession out of people (especially juveniles) and how to take the proper steps to eliminate any holes in evidence (or create a lack thereof) so the case could be airtight and lead to a sentence or at least a plea regardless of innocence.
My father thought it was fucked up but for this detective it was literally the tool he would use to build his career, which he did successfully.
Edit: I should clarify one thing I mentioned. It wasn’t eliminating holes in evidence like planting fake evidence or something like that. He would lock people in an interrogation room for hours and would test to see if people knew their rights. If they didn’t, or weren’t adamant about exercising them, he would be able to keep them locked in without allowing a lawyer or guardian in. When he would get a confession he would book them and force them to sign a written confession, and then all of the video evidence from the interrogation would magically disappear.
It didn’t matter at that point. He got a conviction to his name because most were forced to plea instead of fight it in court.
He would create uphill battles for people who didn’t have the resources to fight.
Мысль на память: Дружба, основанная на бизнесе, лучше, чем бизнес, основанный на дружбе.