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WOBURN — Confirming long-held witness accounts, a report issued Tuesday concluded it is very likely that the MBTA police officer critically wounded in the Watertown shootout with the Boston Marathon bombers was shot accidentally by one of the 19 police officers firing at the suspects.

Marian Ryan, the Middlesex district attorney, said investigators could not determine which gun fired the bullet that struck Officer Richard Donohue, since the bullet remains lodged in his leg and cannot be examined. But a detailed review of the chaotic confrontation with the heavily armed brothers concluded that “it seems highly likely” he was struck by police gunfire meant for a fleeing Dzhokhar Tsarnaev.

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The conclusion that Donohue probably was struck by friendly fire, while long suspected, marked the first official acknowledgment of the cause of his injury. Police witnesses described his shooting during Dzhokhar Tsarnaev’s trial, but no one directly addressed who was responsible.

“It is highly likely that the gun was fired by one of the individuals attempting to stop the armed Dzhokhar Tsarnaev, who was fleeing’’ in a stolen Mercedes-Benz sport utility vehicle, Ryan said at a news conference Tuesday.

“At the time that Officer Donohue was shot, law enforcement officers were firing at the Mercedes from at least three, if not all four, sides,’’ the 19-page report found.

The investigation — which explored the circumstances of the death of Tamerlan Tsarnaev, the possible shooting of Dzhokhar Tsarnaev, and the injury to Donohue — determined that police were “warranted and justified” in using deadly force during the nearly seven-minute shootout on Laurel Street in April 2013.

“Every officer who responded to that situation did so recognizing that they were placing themselves in danger of death or serious bodily injury to come to the aid and defense of their fellow officers and the citizens they are sworn to serve and protect,” Ryan said. “These officers responded in a courageous fashion, which was testament to their commitment and training.”

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Donohue, 35, nearly died from blood loss as a result of the bullet wound, and spent a month in the intensive care unit. He rejoined the force earlier this year, and in May was promoted to sergeant.

Through an MBTA spokesman, Donohue declined to comment Tuesday.

The criminal investigation into the gun battle is now closed, Ryan said.

The inquiry did not review the circumstances of Dzhokhar Tsarnaev’s capture, which happened about 20 hours after the shootout. That scene was under the control of the FBI, the report stated.

In April, a state report by the Massachusetts Emergency Management Agency found that some police officers fired recklessly during the shootout, failing to identify their targets before firing. Many of the officers arrived in Watertown without orders to do so, and the gunfire created dangerous crossfire.

“Weapons discipline was lacking by the multitude of law enforcement officers in the field during both the firefight with the two suspects near Dexter and Laurel streets, and the standoff with the second suspect who was hiding in a winterized boat in a residential backyard,” the state report said.

The results of the investigation released Tuesday provided a detailed narrative of the confrontation, although many aspects had previously been disclosed.

The gun battle began when a Watertown officer located the hijacked Mercedes that Tamerlan Tsarnaev was driving and began to follow it. But as he turned onto Laurel Street, Tsarnaev suddenly stopped, got out of the car, and opened fire on the officer.

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“People began converging on the scene,” Ryan said.

Ryan said the Tsarnaev brothers were heavily armed: in addition to the handgun Tamerlan used to fire on police in Watertown, the brothers detonated two pipe bombs and one pressure-cooker bomb, and had with them but did not detonate two other pipe bombs and what Ryan described as an “improvised explosive device” in the back seat of the vehicle Dzhokhar used to escape the scene.

After hearing gunshots and an explosion, another Watertown police officer, Jeffrey Pugliese, tried to flank the suspects, but Tamerlan charged at him. After they exchanged shots, Tamerlan’s gun apparently jammed, and he threw it at the officer.

The officer tackled him and tried to handcuff him, when he saw the SUV, driven by Dzhokhar, barreling towards him “at a high rate of speed,” Ryan said.

The officer tried to pull Tamerlan to the curb, but was forced to let go of him to avoid being hit by the SUV, which “missed Pugliese by inches.”

The rear wheel ran over Tamerlan, who got caught in the undercarriage and was dragged about 30 feet. As the younger Tsarnaev drove through the intersection of Dexter Avenue and Laurel Street, officers fired at the vehicle from all sides.

Tamerlan Tsarnaev was taken to the hospital, where he was pronounced dead.

In all, investigators recovered 251 cartridge cases, 56 of which were from the gun used by the Tsarnaevs.

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In the Watertown neighborhood where the shooting took place, residents said they were not surprised that Donohue was almost certainly wounded by friendly fire.

“That was my presumption all along,” said Curtis Hazlett, who saw the barrage of gunfire from police from his third-floor apartment. “It was the only realistic possibility, given the way everyone was situated.”

“Everyone is just thankful Officer Donohue did not die,” he said. “What those officers did that night was heroic.”

Another neighbor, Loretta Kehayias, said she was not surprised given the “gunfire going back and forth.”

“It was so out of control, so chaotic,” she said.

Kehayias’s house still shows the holes caused by stray gunfire — a constant reminder to her and her husband, Peter.

“What happened that night is never going to be behind us,” she said.

John R. Ellement of the Globe staff contributed to this report. Peter Schworm can be reached at schworm@globe.com. Follow him on Twitter @globepete.