And for the unaware, he likely resigned so he couldn’t be forced to aid in his own prosecution. Basically, a police department can force an officer to testify against themselves as long as they want to remain a cop. The department basically goes “we’re making your testimony a condition of your ongoing employment. So testify or be fired.” As long as he remains a cop, he doesn’t have a 5th amendment right to remain silent.
By quitting, he’s able to clam up and not aid in any investigation. And since he was given the option to resign instead of being fired, he can simply wait for it to blow over then get the same job in the next city over.