DENVER - Democrats rejected a proposal to make it tougher for Colorado defendants to be found not guilty by reason of insanity by putting the burden of proof on defense attorneys, instead of prosecutors.

A House committee voted 7-4 against the bill Wednesday, citing constitutional and due-process concerns.

Republican Rep. Frank McNulty says the mass shooting at an Aurora movie theater last summer brought his attention to the issue. Lawyers for James Holmes say he's mentally ill, and legal experts expect he'll enter an insanity plea.

At least 30 states put the burden of proof for such claims on defendants, but not Colorado. McNulty says that's unfair to victims.

Colorado's Supreme Court ruled in 1968 that putting the burden on defendants is unconstitutional. Defense attorneys say insanity pleas in Colorado are rare.