A military judge says a U.S. Army psychiatrist cannot plead guilty to any charges in a 2009 shooting rampage at a Texas base.

It was the worst mass shooting on a U.S. military installation.

Maj. Nidal Hasan wanted to plead guilty to 13 counts of premeditated murder. But Army rules prohibit a judge from accepting a guilty plea to charges carrying the death penalty.

Hasan's attorneys had asked the judge to let Hasan plead guilty to lesser charges of unpremeditated murder. He still would have gone to trial in May and faced a possible death sentence if the judge had allowed the plea.

But the judge said Wednesday that Hasan will not be allowed to plead guilty even to the lesser charges.