BOSTON (AP) – House lawmakers soundly rejected Gov. Mitt Romney’s death penalty bill Tuesday, dashing the Republican governor’s hopes of establishing a national “gold standard” for capital punishment in liberal Massachusetts.

Romney had touted the bill as foolproof, saying it would have strict safeguards and seek executions in “very, very rare circumstances,” such as terrorism, serial killing or murdering police officers or other public servants.

But critics in the House said there’s no way to craft a foolproof death penalty bill and that innocent people could still be put to death.

The House defeated the bill on a 99-to-53 vote after more than four hours of impassioned debate. The Senate hasn’t scheduled a debate on the bill.

Rep. Eugene O’Flaherty, D-Chelsea, said scientific evidence presented at trial can sometimes be flawed or misinterpreted because it is gathered and interpreted by people.

“No system that relies on scientific evidence can truly be developed that flawlessly and with no doubt separates the guilty from the innocent,” he said.

Romney, who is weighing a presidential run in 2008, said his plan would have set the nation’s highest standard of proof for ensuring that only the guilty were executed, using scientific evidence such as DNA and multiple checks and balances, including review by the Massachusetts Supreme Judicial Court.

Romney defended the bill Tuesday, calling it the most fail-safe in the country.

“The bill that we put together is exactly as advertised: One that takes out the risk of executing someone who is innocent and it does put in place the ultimate penalty for those who carry out the most horrible crimes in society,” Romney said.

He said he has taken heat from conservatives who feel the bill is too restrictive, but also acknowledged he hasn’t give the bill the same level of attention and lobbying muscle as other issues.

Lt. Gov. Kerry Healey called the House action a “missed opportunity to set a new legal standard” for capital punishment.

“I find this very disappointing. I had hoped that they would have taken a serious look at this legislation and realized that it is unique,” she said moments after the vote.

Romney had pointed to other safeguards in the bill designed to protect the innocent, such as a requirement that physical evidence must directly link the defendant to the crime scene. Only one or two people a year would face the penalty under the bill, Romney estimated.

Some death penalty supporters who voted for the bill said Romney’s legislation was too cautious and should also have included those found guilty of first degree murder or the killing of children.

They said the death penalty would not only deter people from committing murders, but is also fair justice. Without the death penalty, the life of the murderer is given greater value than the life of their victim, supporters said

“Without capital punishment we have devalued an individual’s life. Someone’s got to tell me what a life is worth when that life is snuffed out,” said state Rep. George Peterson, R-Grafton. “What is that life worth when someone takes it? I believe it is worth that person’s life.”

But opponents said the death penalty is unfairly applied to the poor or racial minorities, is too expensive and runs counter to the trend in the world where increasing numbers of countries have abolished capital punishment.

Opponents also said the notion that the death penalty is a deterrent is flawed, given that those convicted of first degree murder in Massachusetts already face life in prison without parole.

“Show me a murderer who decides to kill because he thinks I’m only going to get life in prison,”‘ said Garrett J. Bradley, D-Hingham.

During the debate, lawmakers recalled stories of family members and friends who had been murdered while others told of their experiences as prosecutors who investigated and tried those accused of murder.

Death penalty bills have faced increasing opposition from state lawmakers in recent years.

Support for capital punishment peaked in 1997 following the gruesome abduction and murder of 10-year-old Jeffery Curley of Cambridge.

The House, after a wrenching debate, initially approved the death penalty by one vote that year. On a final, procedural tally, a single House lawmaker, Democrat John Slattery of Peabody, changed his mind, killing the measure.

Since then, the margin of opposition has steadily grown in the House, which defeated another death penalty bill two years later by 80-73 margin.

In 1982, 54 percent of Massachusetts voters approved a death penalty ballot question, which was later ruled unconstitutional by the state Supreme Judicial Court.

Massachusetts is one of just a dozen states without capital punishment. The last execution here was in 1947.