Hoping to bring capital punishment to Massachusetts, Gov. Mitt Romney (search) is preparing to file a death penalty (search) bill early next year that he says is so carefully written it will guarantee only the guilty are executed.

Based in part on the findings of a death penalty panel he appointed, the bill would limit capital punishment to the "worst of the worst" crimes including terrorism, the murder of police officers, murder involving torture and the killing of witnesses. It also would use evidence such as DNA testing (search) to protect the innocent.

Romney wants his death penalty bill to be a model for other states.

"The weakness in the death penalty statutes in other states, of course, is the fear that you may execute someone who is innocent. We remove that possibility," Romney said.

Massachusetts is one of a dozen states without capital punishment. The bill fulfills one of the Republican governor's key campaign pledges, but faces a skeptical Democrat-controlled state Legislature.

"I don't believe it's possible to be 100 percent certain no matter what you do. Humans are fallible," said state Rep. Elizabeth Malia, a Democrat.

Rep. Michael Festa, a Democrat, said Romney should focus on crimefighting tactics that work, like a proposal to support community-based drug treatment programs. A member of the Criminal Justice Committee, he said he hopes Romney's death penalty bill makes it to the floor of the House for a vote — so it can be defeated.

"I think we should stand up as lawmakers and say we don't want this in our state," he said.

Romney said he based the bill in large part on the recommendations of the death penalty panel he appointed.

The report called for creation of an independent committee to review all scientific evidence in a case. It proposes giving defendants in capital cases better lawyers and the opportunity to face two juries, one for the trial, and if convicted, a separate one for sentencing.

It also suggests doing away with the legal standard of guilt "beyond a reasonable doubt" in a death penalty case, and replacing it with a finding of "no doubt."

Even Romney concedes that it might take a horrific crime, like the 1997 murder of 10-year-old Jeffrey Curley, to rally support for the bill.

Curley was abducted from a Cambridge street and killed by two men who later received life sentences. Public outrage fueled calls for a death penalty bill that passed easily in the state Senate; it was defeated by a single vote in the House. Since then the margin has grown in the House, which defeated a death penalty bill two years later, 80-73.