A Massachusetts police officer described to a Fredericton courtroom Wednesday how he arrested Gregory Allan Despres, 24, after the U.S. Federal Bureau of Investigation issued a lookout, saying he was a "person of interest" in the gruesome double-homicide of an elderly New Brunswick couple.

Sgt. Jason King, of the Mattapoisett police department, told the court he was working an evening shift on April 26, 2005, when an FBI message came over the police computer, warning officers that a potentially dangerous murder suspect was heading his way.

King testified the message caught his attention because he knew Despres from six years previous, when the young man lived in Acushnet, Mass., a small community south of Boston. "He worked at the marina where I actually keep my boat. So I'd see him there."

Despres is accused of violently and fatally attacking his Minto neighbours, Fred Fulton, 74 and Verna Decarie, 70 on April 23, 2004 — three days before officers arrested him in the United States. Despres has pleaded not guilty to both crimes.

Officer went to marina

Immediately after receiving the message from the FBI, King told the court he drove to the local marina, and asked the owner if he had heard from Despres or was expecting him.

King testified that the FBI lookout warning was "more than enough reason" to arrest Despres.

"I wasn't about to let this man walk through town if he was wanted for a double homicide," he said. "For the safety of the citizens, I wasn't going to let him walk around."

The marina owner gave King the name of one of Despres's relatives in the area. King then drove back to the police station, obtained a copy of an RCMP warrant and a package of photos and other information from the Maine border office, where Despres crossed into the U.S. the day before.

King quickly sent out the information package to officers in the immediate area, and to police in surrounding communities.

Officer spotted Despres on highway 

Not long after, Officer Andy Murray called King for backup, advising that Despres had been seen walking along Highway 6, not far from the police station.

"He [Murray] notified me he had Mr. Despres under surveillance. He was watching him. He requested me come to the scene for backup," he said.

King testified he drove to the scene, where Murray was parked at a restaurant, watching Despres walk along the road.

More cruisers arrived from the neighbouring community of Fairhaven, to provide backup, and King testified he and another officer jumped out of their cruisers and arrested Despres without incident, handcuffing him and seizing all of his belongings, including his wet and dirty clothing.

King is one of eight American law enforcement officers scheduled to testify at Despres's first-degree murder trial, now in its second week in Fredericton.

The officers are testifying in a voir dire hearing to determine the admissibility of their evidence. Judge Judy Clendenning has not ruled whether the testimony will be evidence, but has not banned publication.

The trial continues Wednesday afternoon.