PROVIDENCE, R.I. – A Providence detective was killed with his own gun at police headquarters yesterday by a suspect who was not handcuffed and managed to get hold of the weapon, the police chief said.

The killing of James Allen, a 27-year veteran, comes after a series of attacks that have raised concerns about the security of those who work in the criminal justice system.

Allen, 50, was shot in the detective conference room while questioning Estenban Carpio about the stabbing of an 84-year-old woman who survived the attack, Chief Dean Esserman said. Mr. Carpio was not under arrest and had been taken out of handcuffs, he said.

Mr. Carpio, 26, allegedly grabbed the officer’s gun, shot him, broke a third floor window in an adjacent office, and jumped onto a service road, Mr. Esserman said at a news conference. He was captured after a struggle a few blocks away and charged with murder last night. The chief would not say how Mr. Carpio managed to get Allen’s weapon, and would not discuss other details leading up to the shooting, including whether there were witnesses.

“The investigation has begun and we will find answers, but not here this morning,” he said.

Mr. Esserman also would not discuss the protocols for carrying weapons inside police headquarters, or for interviewing potential suspects.

Allen, who was married and had two daughters, was pronounced dead at a hospital shortly after the shooting.

Paul Kennedy, the deputy police chief, said Allen was an experienced investigator, one of the department’s longest-serving detectives. His father is a retired police captain.

“Jimmy Allen passed in the noblest way possible. He gave his life trying to make our lives safer,” said Mayor David Cicilline. “He died a hero.”

Security in government buildings has been a greater concern since March, when a man in the middle of a rape retrial in Atlanta allegedly overpowered a court deputy and took her gun, then killed the judge presiding over his case, a court reporter, a deputy outside the courthouse and a federal customs agent.

Just weeks before, the husband and mother of a Chicago federal judge were slain in her home.

Visitors to the Providence police building must pass through a metal detector since last fall, when a man walked into the lobby with a loaded gun and told an officer he might hurt himself or someone else. Officers disarmed him and no one was hurt.

An expert in police procedures who teaches at Salve Regina University in Newport, Michael Brady, said every police station has areas called “weapons secure,” where guns are banned. These generally include cell blocks and interrogation rooms, he said, but not areas such as detective conference rooms.

But if Allen wanted to question Mr. Carpio, Mr. Brady said, it would not have been unusual for him to do so in a nonsecure area with his gun in his holster.

“This officer was not doing something very different than what police officers throughout the nation do every single day,” he said.