Of particular concern is the legal concept known as "presumption," which prosecutors say could force juries to "presume" it was necessary to kill someone despite the evidence, The Dallas Morning News reported Monday.

Known as the castle law, the year-old measure says a citizen is "presumed" to be acting reasonably if he shoots someone he believes is trying to break into his occupied home, business or car.

Prosecutors worry that the law could result in a murderer being let off the hook.

"We have some very good defense attorneys in Harris County, and they're going to have an absolute field day with this," says Bill Delmore, an assistant district attorney in Harris County.

So far, the law hasn't been tested in court but homicide cases affected by it could emerge by the middle of this year, say prosecutors.