When a police officer is slain, the stakes go up. Suspects often face the death penalty and all parties operate under intense scrutiny and high publicity.

That will be the case this morning when a Mount Oliver man goes on trial in the killing of a Pennsylvania state trooper. Allegheny County District Attorney Stephen A. Zappala Jr. is seeking the death penalty, a decision law enforcement groups applaud.

"I don't think the life of any human being is greater than any other," said Craig Floyd, chairman of the National Law Enforcement Officers Memorial Fund. But "it's imperative we do everything possible to make sure our officers are safe, and part of that equation is having deterrents against assaulting and killing police officers."

Some death penalty opponents say cop killings cause prosecutors to pursue defendants to the fullest extent of the law.

"In instances when a police officer is tragically slain, there is greater political pressure not only to pursue a death sentence but to see that a death sentence is carried through all the way to execution," said David Elliot, spokesman for the National Coalition to Abolish the Death Penalty.

In states with a death penalty, laws specify that killing an officer is an aggravating factor that can qualify a homicide as a capital offense. The killing of an officer of the state is often treated as an attack on the state itself, so such homicides carry the weight of the state, as well as of an individual as victim.

Samuel H. Pillsbury, a professor at Loyola Law School and former federal prosecutor in Los Angeles, said when officers are slain the cases are "sort of automatically high-profile."

"Anytime a police officer is a victim absolutely everything on the law enforcement side gets ratcheted up. There are a great deal more resources put into the investigation. Lab work gets done right away. Officers are pulled off other cases. Interrogations are handled differently," he said. "It's an attack on the system itself, so everyone in the system, especially prosecutors, takes it seriously."

The killing

At about 2 a.m. on Dec. 12, 2005, a Carnegie police sergeant came upon a parked state police patrol car with the driver's door ajar and the overhead red-and-blue lights spinning. He found the body of Cpl. Joseph R. Pokorny Jr. in a snow bank 25 feet away. The trooper died of a bullet wound to the chest and also was shot in the back of the head. The slugs were traced to his own department-issued Beretta.

The Moon resident and divorced father of two had been patrolling the Parkway West when he pulled over a speeding car near the Extended Stay America Hotel in Carnegie and a struggle ensued. He was the 91st trooper to die in the line of duty since 1905.

Amid a massive sweep of city neighborhoods, police arrested Leslie Denier Mollett on a parole violation. He'd been released from prison on drug charges less than a month before. Within days of the killing, Mr. Mollett was charged with homicide, firearms violations, theft, disarming a law enforcement officer, fleeing or attempting to elude, and resisting arrest.

Defense attorney John Elash agrees that his client was stopped by a patrolman on the Parkway West, but says Mr. Mollett had nothing to do with the shooting of the 22¹/₂-year veteran trooper.

Mr. Zappala, who has charged 29 defendants with capital homicide since 1998, declined to comment on his choice to pursue the death penalty in the Mollett case. It will be his administration's first capital prosecution involving a slain officer, but it is relatively unusual that a homicide victim is a uniformed police officer.

"Generally speaking, every potential capital case is reviewed based on the facts that are specific to that case. There is no boilerplate set of circumstances that determines when I choose to seek the death penalty," he said.

Mr. Elash, a veteran trial lawyer who has defended about 20 capital cases, said, "I don't think [Mr. Zappala] should have sought the death penalty in this case because this was a happenstance event that just occurred. How do you have a cold-blooded plan to be pulled over by a state trooper on a highway and to shoot him?"

He said a video camera attached to the patrol car was automatically filming the traffic stop and several motorists could easily view the scene.

"Whoever did it, it wasn't a calculated plan," he said.

The trial

Although he is presumed innocent, Mr. Mollett, 32, is up against daunting odds today when the lawyers present opening statements and the prosecution begins its case. In the past decade, one of four defendants found guilty of killing an on-duty officer got a death sentence, according to FBI crime reports.

Research by a prosecutor in Indiana shows that 27 of the 85 death row inmates executed since 2000 were convicted of killing law enforcement officers.

"My opinion is you're more likely to be executed if you kill a police officer. I think the public, which makes up the jury, knows that only the worst of the worst would kill a police officer," said Clark County prosecutor Steven D. Stewart, who posted online victim profiles for each execution. No federal agency maintains data that could corroborate his findings.

Richard Dieter, who heads the nonprofit Death Penalty Information Center in Washington, D.C., said that in public discourse killing an officer is "the prime example of a case people point to where they say you need the death penalty."

Kansas legislators cited cop killings as a reason for bringing back the death penalty in 1994, he said; however, he said, capital convictions are not always sought in these cases, "despite the common belief."

Three men have been killed by lethal injection since capital punishment was reinstated in Pennsylvania, none convicted for killing an officer. Eleven of the 228 inmates on death row were convicted of killing active or off-duty police officers, said Susan McNaughton, spokeswoman for the state Department of Corrections. A 12th inmate was convicted in the death of an off-duty prison official, she said.

Cpl. Pokorny's death sparked an outpouring of support and court officials expect state troopers will turn out in big numbers for Mr. Mollett's trial, as fellow officers typically do in such cases.

"By killing a police officer you have gone against the very fabric of our liberty and our democracy," said Bruce A. Edwards, president of the Pennsylvania State Troopers Association.