CONCORD — The New Hampshire Supreme Court on Thursday ruled that a jury fairly handed down a death sentence to a man convicted of killing a Manchester police officer nearly a decade ago.

The justices of the state's highest court unanimously ruled that Michael Addison will remain the state's only death row inmate. He was convicted of killing officer Michael Briggs after a violent, weeklong series of crimes in October 2006 that put him at the top of the city's "most wanted" list.

In their first fairness review of a death sentence, the justices compared the Addison case to others across the country in which a person was convicted of killing a police officer in the line of duty.

"We conclude that the defendant's sentence is neither excessive nor disproportionate and, accordingly, affirm his sentence of death," the justices wrote.

His lawyers had argued the Briggs killing lacked the brutality of other killings.

Addison's lawyer says he's considering asking the court to reconsider its nine-page ruling.

"As lawyers, we value highly the process that leads to the result," said David Rothstein, Addison's lead lawyer. "Our work was arduous and it was comprehensive. Unfortunately, while the decision states a result, it does not do justice to the process."

On Oct. 16, 2006, Addison was wanted by police for a string of violent crimes, including several armed robberies and a drive-by shooting. Briggs was 15 minutes from the end of his shift when he and his partner — both on bicycle patrol — confronted Addison in a dark alley. Jurors found that Addison shot Briggs in the head at close range to avoid arrest.

During appeal, Senior Assistant Attorney General Jeffery Strelzin argued that criminals who kill police officers "demonstrate in the most extreme way possible that they have no respect for the rule of law or for human life."

"It is no surprise that criminals like the defendant who murder law enforcement officers acting in the line of duty are more often sentenced to death," Strelzin wrote in his brief.

During arguments in January, Justice Gary Hicks pointed out that Briggs had asked Addison to stop more than once, then, as Briggs approached him, Addison held his hand up, "it could be argued, ensnaring Officer Briggs in a trap, then put a bullet through his bike helmet. Why isn't that heinous?"

Strelzin said Thursday the ruling is a relief to the Briggs family and the Manchester police department.

"This has been an incredibly long process for them and they continue to bear the burden every day of what the defendant did to Michael Briggs," Strelzin said.

Addison's lawyers argued that the court should review about 350 death penalty cases from 25 other states, but the court adopted the state's position that 10 cases in which officers were killed in the line of duty were most similar to the circumstances of the Briggs killing.

The justices concluded that no two capital murder defendants are alike, but stated, "Our function is to identify an aberrant death sentence, not to search for proof that a defendant's sentence is perfectly symmetrical with the penalty imposed in all other similar cases."

While Thursday's ruling is the last of Addison's direct appeals to the state Supreme Court, defense lawyers are already mobilizing in an effort to undermine the foundation of his death sentence.

Defense attorney Richard Samdperil filed an appeal of one of Addison's convictions for a robbery in the days leading up to the Briggs shooting. Prosecutors used that robbery and others in his violent crime spree as aggravating factors in arguing for a death sentence. If Samdperil can upset one of those factors, it could trigger a fresh analysis of Addison's death sentence.

The new appeal, filed April 6, claims Addison's trial lawyers were at fault for not questioning the 11th-hour assignment of Judge Kathleen McGuire to the case and her failure to postpone the trial when prosecutors filed newly-discovered evidence on the eve of trial.