EDITORIAL There's a good reason that not too many police chiefs become district attorneys. Obviously, not a lot of cops have law degrees, but it goes beyond that. The district attorney is supposed to monitor the police, to investigate criminal behavior by cops, to make sure the people out on the streets aren't doing anything that will screw up cases in court.

But that didn't bother former Mayor Gavin Newsom (who apparently doesn't think that conflict-of-interest statutes apply to him). Newsom appointed Gascón to the D.A.'s job despite some serious concerns about the operations of the Police Department — and problems at the SFPD have blown up yet again. Four times in the past two weeks, Public Defender Jeff Adachi has released videotapes showing undercover cops entering residential hotel rooms without a warrant. The videos appear to contradict the information that the officers presented in their written reports, and the pattern of conduct has caused interim Chief Jeff Godown to suspend the entire undercover narcotics unit at Southern Station.

It's also caused the District Attorney's Office to undertake an investigation. And no matter what comes out of that inquiry, it will be fatally tainted by the fact that Gascón is, in effect, investigating his own operation.

Gascón hired Godown, who came from Los Angeles. He was, until just three months ago, in charge of the department that's apparently running amok. The problems that have surfaced didn't just emerge the day Gascón left; for all practical purposes, they are his problems, coming from his department, growing and festering under his watch.

A serious investigation would not only look at the actions of this one handful of officers, but at the command structure and climate that allowed this sort of behavior to become routine. It would look at the chain of command all the way to the top — that is, to the chief. To Gascón.

The D.A.'s office can't possibly get this right. If Gascón finds wrongdoing on the part of these particular officers, the officers will no doubt seek to have the investigation and any prosecution set aside on the grounds that the former chief was a conflict. If he finds no wrongdoing, it will look like a cover-up.

This is only the first of what could be a long series of conflict problems with Gascón's office. Put simply: the former chief can't effectively monitor the police department, particularly if there are allegations of misconduct that come from the era when he was in charge.

There's no easy way around this. Gascón could (and probably should) recuse himself and his office, and ask the attorney general to conduct the investigation. But the A.G.'s office doesn't have a great track record on taking over local cases like these. His only real alternative is to hire an independent outsider — the equivalent of a special prosecutor — to handle all cases involving the police department. That would be expensive, but it's the result of the unfortunate, highly unusual situation that Newsom and Gascón created.