You can read Sanjuro's concise summary of the police officers' allegations here and view their videos -- collected in one place -- here. The videos are in Russian, but seeing them all together on one web page gives you the strong impression that something important is happening. After examining the evidence, Sanjuro makes an intriguing observation: "I do not exclude the possibility that at least the initial impulse of this movement could be engineered within a liberal wing in Medvedev's surrounding as a (belated) attempt to improve the public image of the police (which is frankly, beyond repair)."
This spectacle certainly caught me off guard. I was not aware that Russia had much of a whistle-blowing tradition. So I put this question to Sanjuro: Why have so many officers have come forward, risking their careers. Surely they were put up to it?
No, Russia doesn't have much of a whistleblowing tradition. It is extremely rare and hence deserves respect even if there's some degree of support from the superiors. On the other hand, just four people in the entire country is not enough.
I would believe these people were identified earlier by some senior officers from the SK (Sledstvenny Komitet) of the Prosecutor General's office that is independent (at least officially) from the MVD, they were advised that if they came out exposing corruption at the local branches, they would be given some justice and protection. There were several PR disasters lately, with the Russian police, most notably the Maj. Yevsyukov incident (a drunken policeman shot several people in a grocery store), several road accidents where policemen escaped justice, extrajudicial killings etc etc. Plus regular reports of police brutality, incl those during the dissident gathrings. It was also reported recently that the Russian riot police tested their new fancy toys on a mock demonstration of "senior citizens" - which was later denied.
If it's Kremlin-engineered, it is a smart move, and a chance for Medvedev to earn some real political capital, not inherited from Putin. The public outcry in April was such that the head of the Moscow police Gen. Pronin had to be removed as a result of the Yevsyukov affair - I guess it was then that somebody in Medvedev's circle realized that something has to be done urgently about the police. Whatever the origins, this could have real consequences, as more people both within the police and outside will be urged to speak out.