A New York Times article recently addressed the issue of cops lying under oath.
This is actually a much bigger problem than you would think. Cops make stops and arrests without justification and then lie in their reports. Then they lie to prosecutors during prefile conferences. And then to defense attorneys during depositions. And then before juries in trials and judges during motion hearings.
As a defense attorney I have tried to figure out why cops lie. Not all of them lie. In fact, most of them are just doing their jobs. But a good number of them will deliberately omit valuable information from their reports and testimonies, embellish facts, or just outright lie about how an incident occurred. And what's troubling is that police officers have no personal stake in a case. They are simply doing their jobs. If a crime is committed and evidence supports it, so be it.
But some officers, especially working street-level investigations involving the sale of drugs, seem to disregard suspects' rights, doing whatever they please just to make an arrest. Only later do the officers justify their actions, legally speaking, in their reports and subsequent testimony.
Very interesting article, perhaps giving a much-needed explanation as to why police officers feel the need to lie.