Stupid cop trick #410:
Only videotaping interrogations if a suspect is being cooperative, that is, has already confessed during the 'pre-interview.' They 'say' they give rights warnings before even the pre-interview, but with no video or audio, there’s no way to corroborate the timing of the rights waiver.
They used to do the pre interview and then give a rights waiver only if they got a confession, but Siebert has cut down on that some, subject to the same verifiability problems.
There are all sorts of tricks an interrogator can use in a pre-interview: they can threaten to incarcerate family or friends, they can feed the suspect details of the case for the suspect to parrot back after they're "cooperative," they can take care of any concerns a suspect may have about their right to counsel and explain away the suspects concerns, they can get the suspect to confess to self-defense or some lesser offense, etc.
There really isn't a downside to unrecorded pre-interviews; the final, recorded interrogation is smooth and error free. If a suspect 'cooperates' and then clams up for the recorded section (because the pressure's off, or there's a different pair of interrogators) the police can testify as to what they think the suspect said; who is a jury going to believe, a cop or a murderer/rapist, etc.?
But how to cut down on the practice of unrecorded interrogations until a suspect is "cooperative?" The S.Ct of Minnesota has a reasonably workable rule. Scales, 518 N.W.2d 587 (MN, 1984), requires cops to videotape ALL interrogations unless there's some reason not to. Alaska has something similar, and Illinois and Maine have done it by legislation.