A State Police trooper fatally shot a man on a footbridge over Storrow Drive near Boston University on Friday afternoon after the man allegedly refused to drop a knife and made threats, unnerving passersby in the well-traveled area, officials and witnesses said.
The confrontation — witnessed by several pedestrians and by motorists including Boston’s former police commissioner — began shortly after 2 p.m., when BU police officers on the Esplanade spotted a man who matched the description of a suspect with outstanding warrants out of Roxbury District Court, State Police Colonel Timothy Alben said.
Suffolk District Attorney Daniel F. Conley’s office, which is investigating the shooting according to standard protocol, identified the man Friday night as Santos Laboy, 45, of Somerville.
Laboy fled when police approached him, Alben said, at one point running onto busy Storrow Drive, which borders the Esplanade and the Charles River, then running back into the park.
“It appears he brandished a knife” during the pursuit, Alben said, and was “waving it about.”
Laboy ran up onto the footbridge, where he encountered the uniformed state trooper, who had been working a nearby detail and came to assist, officials said.
Laboy and the trooper exchanged words on the bridge, Alben said, and the trooper ordered him to drop the knife, but he refused and made “threatening gestures.”
“There were shots fired at that point,” Alben said.
A distraught woman who answered the phone Friday night at a Boston address listed for Laboy’s mother said, “yes, my brother was killed” and added that she believed he had a small knife with him. She declined to comment further.
Former Boston police commissioner Edward F. Davis said in a telephone interview that he was driving on Storrow Drive on Friday afternoon and witnessed the pursuit of Laboy and the fatal shooting.
Laboy “ran up the walkway and the officers were telling him to ‘Drop the knife! Drop the knife!’ He didn’t drop the knife,” said Davis, who is a security consultant for the Globe.
“Then there was a trooper who had come from the other side of the walkway,” Davis said. “The guy went at him. The trooper said, ‘Drop the weapon! Drop the weapon!’ The trooper then fired at him when he refused to drop the weapon.”
Laboy was pronounced dead at the scene after police and paramedics attempted to revive him but were unable to do so, State Police said.
Alben declined to say what words were exchanged between Laboy and the trooper. Jake Wark, a spokesman for Conley, confirmed that Laboy was the man with the warrants out of Roxbury District Court. Alben, who had described the suspect as possibly white or Hispanic, said the warrants were for charges including harassment and annoying a person of the opposite sex.
Laboy has “a substantial and long criminal history, primarily here in Suffolk County,” Alben said.
He declined to say how many shots the trooper fired or where Laboy was struck.
David Procopio, a State Police spokesman, said investigators recovered the knife that Laboy allegedly wielded, but he could not say how large it was.
Laboy frequented the Esplanade, and a Boston police intelligence gathering unit had informed area departments Friday that he was being sought, Alben said.
According to court records, Laboy was convicted in 2010 in Suffolk Superior Court on charges of carrying a dangerous weapon, assault with a dangerous weapon, and malicious destruction of property.
He was charged as a habitual offender in that case and sentenced to a maximum prison term of five years, court records show. While the case was pending, his lawyer requested funds for a mental health evaluation, according to the case docket.
Jorge Laboy, 47, of Brockton, a cousin of Santos Laboy, said relatives told him that Santos was homeless and had been fired from a job. He said he had been told his cousin had mental health problems after coming out of prison and recently told his sister that “he’s not going back to jail, [and] they’re going to have to kill him.”
Santos Laboy grew up in Boston and his father, who had the same name, owned a liquor store in the city before he died several years ago, Jorge Laboy said.
Laboy had recently posted combative messages on his Facebook page, including one directed at law enforcement officials on June 3 that said, “Despite your threat to use force to capture me if I refuse to surrender, I’m still free and getting stronger by the day. Got nothing to lose.”
On Friday night, relatives offered condolences on Facebook and hinted at his personal struggles.
A woman who identified herself as a cousin wrote that “he needed help in so many ways” and said Santos was “at peace now. I’m so sorry we lost you.”
On Friday, a witness to the shooting, Samantha Bourdeau, 22, said she was riding in a car on Storrow Drive when she saw a man on the road, and “the next thing you knew, you look directly up and he’s on the bridge.” She said she saw police shoot him multiple times and heard at least three consecutive “booms” from the gunfire.
BU graduate student Chelsea Reid said she saw a shirtless man running along the Esplanade and said several officers jumped out of a van and gave chase.
The officers yelled, “Take him down! Take him down!” Reid said. “I’m shaken up. . . . It’s just a lot.”
The shooting came 2½ weeks after Boston police and FBI agents from a Joint Terrorism Task Force shot and killed Usaamah Rahim, 26, of Roslindale, who had allegedly lunged at the investigators with a military-style knife.
Rahim had been under 24-hour surveillance on suspicion of plotting to attack people in the United States in support of the Islamic State
An FBI spokeswoman said the shooting Friday was not related to any terrorism investigation.
Conley said his office will determine whether the use of force was justified based on “a full, fair, and impartial investigation. We draw no conclusions from the preliminary evidence and we reserve judgment until all the facts are in.”
Bourdeau, the witness who saw Laboy make his way from the street to the bridge, said the vehicle she was traveling in was under the bridge during the altercation and that she heard yelling before the gunshots.
“It was so scary,” she said. “When I close my eyes, I still see it.”
Mike Bello, John R. Ellement, Martin Finucane, and Catherine Cloutier of the Globe staff and Globe correspondents Monica Disare and Aneri Pattani contributed to this report. Travis Andersen can be reached at firstname.lastname@example.org. Peter Schworm can be reached at email@example.com. Follow him on Twitter @globepete. Sara DiNatale can be reached at firstname.lastname@example.org.