KATHERINE JACKSON: I Need Help from the Doctor Who Killed My Son

Katherine Jackson is reaching out to the man who killed her son because she needs him badly for something ... TMZ has learned.

Katherine is in the throes of a wrongful death lawsuit against AEG, claiming the company negligently hired Dr. Conrad Murray and failed to properly supervise him.

Here's the problem.  She needs Murray on the record, explaining how the arrangement went down, so she's subpoenaed the jailed Doc. Katherine wants Murray to acknowledge AEG masterminded the plan to bring him on board.

It's ironic, to say the least, but Katherine is dealing with some bad options. She can go after Murray, but he doesn't have a pot to piss in. Or, she can try to bring him into the fold in order to go after the deep pockets -- AEG.

Now the real problem -- Murray's not cooperating. His lawyers, Valerie Wass and J. Michael Flanagan, are fighting the subpoena, trying to get it tossed on technical grounds.

So Katherine can persist ... and a judge could order Murray to tell all. But she doesn't want to unnecessarily antagonize the Doc, because a hostile witness is often a bad witness.