It's one of the most common accusations by defendants and defense attorneys -- that police officers don't tell the truth on the witness stand.

Of course, defendants themselves can be the ones lying, but the problem of police perjury -- and what can be done about it -- is being debated anew. Fueling the discussion are recent court cases in New York City and Boston that indicated officers may have lied and a U.S. Supreme Court ruling this month that could have broader implications for cases in which improperly obtained evidence...