Suffolk County District Attorney Daniel F. Conley today announced that his office would not seek criminal charges against an off-duty special police officer who shot and killed a man during a knife attack at a downtown Boston medical suite late last year.

“Paul Langone acted in self-defense and the defense of Dr. Astrid Desrosiers when he fired on Jay Carciero,” Conley said. “But for Mr. Langone’s actions that day, she would undoubtedly have died and others – including Mr. Langone himself – could have been seriously injured or killed as well.”

Langone shot and killed Carciero shortly after 2:00 p.m. on Oct. 27, 2009, when Langone interrupted Carciero during a brutal knife attack upon Dr. Desrosiers inside her office at 50 Staniford St. Carciero had turned toward Langone with the knife in his hand when Langone fired three shots, striking him with two and causing fatal injuries.

Conley delivered his findings after five months of investigation and legal analysis by senior members of his Homicide Unit and Boston Police homicide detectives. Prosecutors reviewed relevant case law as well as investigative reports, medical records, recorded witness statements and 911 calls, ballistics evidence, background information on the principals, and other materials developed by detectives.

Notably, investigators could discern no motive for Carciero’s attack upon Dr. Desrosiers. He did not speak to her in the moments before the attack. He had not previously given her a reason to think he would become violent. He did not contact her on Oct. 27 prior to his arrival at her office.

“By every account we reviewed, Mr. Carciero’s actions that day were entirely out of character,” Conley said. “He was known in his community as a devoted father and a loving husband. There was nothing in his background to suggest that this event was coming. We recognize his family’s terrible loss and the tragedy it represented for those who knew and loved him.”

Under Massachusetts law, the legal use of deadly force in self defense requires that the user have a reasonable apprehension of suffering death or great bodily harm and a reasonable belief that no other means would prevent such harm. Based upon their review, prosecutors found that Langone believed he was in immediate danger of being stabbed by Carciero and had no way to avoid that attack except by use of his properly licensed Glock 27 handgun.

The legal use of deadly force in the defense of another requires that the user reasonably believe his action was necessary to protect a third party and that the third party would be justified in using deadly force to protect herself. Based upon their review, prosecutors found that Dr. Desrosiers would have been justified in using deadly force if she were able to do so, that she was completely incapacitated when Langone took action on her behalf, and that Langone’s actions were necessary to protect her from further injury.

As part of their legal review, prosecutors also considered whether Langone’s use of deadly force was excessive in light of the circumstances. Under Massachusetts law, the excessive use of force in self-defense or defense of another can constitute manslaughter. Given the ongoing and brutal attack against Dr. Desrosiers and Carciero’s advance on him, Langone had no other reasonable means of protecting himself and Dr. Desrosiers. Prosecutors therefore found no evidence of excessive force.

“Mr. Langone acted out of necessity,” Conley said. “At no point did he take an action that was not reasonable or required by the circumstances in that room.”

Prior to reaching their legal conclusions, prosecutors studied the facts and circumstances before, during, and after the fatal shooting. Those facts and circumstances are as follows:

Both Langone and Carciero had scheduled appointments on the fifth floor of 50 Staniford St., which holds several medical, dental, research, and mental health offices. Because Carciero arrived well in advance of his appointment and appeared anxious, Dr. Desrosiers saw him at 2:00 rather than the scheduled time of 4:00.

Shortly after entering Dr. Desrosiers’ office, and with no provocation or explanation, Carciero produced a Smith & Wesson Extreme Ops model folding knife with a 4” blade and began to stab her. Two doctors heard her screams and entered the office, observing Carciero straddling her and stabbing her repeatedly. With his hands covered in the doctor’s blood, Carciero then chased both men out of the room with the knife, slashing at and injuring one of them. He then resumed his attack upon Dr. Desrosiers, who lay on the floor.

Having heard her rising screams, Langone left the fifth floor reception area where he was seated and approached Dr. Desrosiers’ office. When he opened the door, he observed Carciero atop Dr. Desrosiers. Dr. Desrosiers was on the floor with multiple stab wounds to her chest and neck. Carciero was about 6’ tall and weighed about 220 lbs. He was still stabbing her when Langone entered the room.

Langone identified himself as a special police officer and ordered Carciero to stop what he was doing. He spoke loudly enough that people outside the room could hear him. Carciero did not comply with those orders. Langone produced his handgun and again ordered Carciero to stop, saying, “Put down the knife, I’m going to shoot.” Carciero turned toward Langone and lunged at him with the knife in his hand.

Langone fired his handgun as Carciero continued to advance toward him. Langone fired a total of three shots, striking Carciero once in the head and once in the abdomen. It was only after these shots that Carciero stopped and fell to the ground.

Carciero suffered no other injuries during the incident. The Office of the Chief Medical Examiner deemed the cause of Carciero’s death to be multiple gunshot wounds and the manner of his death to be homicide.

After Carciero fell, Langone again identified himself as a special police officer and asked that 911 be called. He cleared his weapon and placed it on the floor, then placed it back in his waistband to maintain custody of it as more civilians approached. He assisted in first aid efforts by office personnel.

When Boston Police arrived moments later, Langone identified himself as the shooter and a special police officer. He put his hands in the air, complied with all police orders, and directed officers to the firearm at his waistband. He consented to an interview with homicide detectives and gave a full statement at Boston Police headquarters.

Langone was employed by U.S. Security Associates as a special police officer. At the time of the shooting, he was not on duty and not on the premises at which he had law enforcement powers. The Glock 27 he carried that day was his personal weapon and not his service revolver. The Glock had been legally purchased, properly registered, and licensed for concealed carry.

“For all legal purposes, Mr. Langone was a civilian that day,” Conley said. “He was an ordinary person thrust into extraordinary circumstances. He saved Dr. Desrosiers’ life and possibly others, including his own. There are no legal grounds for criminal charges in this incident, and we consider the case closed.”