Actually I answered it a few pages back, but here it is again, and no worries thcheaven, fdd and I aren't fighting... he's like a brother to me
and I do agree rioting and calling the officer a cold blooded murderer aren't going to solve anything... not a one of us knows for sure and we won't until the trials over a long time from now.
By resigning his position, the BART officer made the tactical decision that it was better to do so than to refuse a direct order to talk about the case to his department's Internal Affairs division. If he'd waived his rights and spoken with the IA investigators, his statements would be used against him in any future criminal proceedings. If he refused to waive his rights, but provided details about the incident after being ordered to, he might still have those statements used against him in Federal violation of civil rights criminal trial, possibly in criminal trial in state court (there's some recent cases allowing this) and would certainly have those statements used against him in civil (state or federal) court. A refusal to talk at all would have led to automatic termination.
Any way you look at it, resignation was probably the best tactical decision for him at the time (given the circumstances), since he's a lot more concerned about the
threat of criminal prosecution (possibly just to "calm" the public?) than his employment at this point.