BOSTON (CBS) – An MBTA police officer was shot and seriously wounded early Friday morning while chasing the two men wanted for the Boston Marathon bombings.

Officer Richard Donohue, Jr., 33, was rushed to Mount Auburn Hospital in Cambridge, where he is in critical condition.

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Donohue has been with the department for three years.

A chaotic chase through Cambridge and into Watertown began with the fatal shooting of an MIT police officer at about 10:30 p.m. Thursday.

According to WBZ-TV’s Joe Shortsleeve, MBTA transit police intercepted the brothers who were driving a Mercedes in Cambridge and followed it.

A source told Shortsleeve the brothers lost control of the car and crashed it. A gunfight with police erupted and Donohue was shot and seriously wounded.

CBS News Senior Correspondent John Miller reported that Tamerlan Tsarnaev threw a bomb at police as he approached them and that’s when officers shot and killed him.

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Shortsleeve’s source said Dzhokhar Tsarnaev then jumped back in the Mercedes, drove over his brother’s body, threw bombs at police and crashed again.

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He ran off, firing a weapon and that sparked the massive manhunt in Watertown.

The MBTA said Donohue and murdered MIT officer Sean Collier graduated from the same Municipal Police Officers’ Training Academy class.

“Facing extraordinary danger, Officer Donohue never hesitated in fully engaging the terrorists in order to protect the citizens of the Commonwealth,” said MBTA Transit Police Chief Paul MacMillan. “I am extremely proud of him, and cannot say enough about his heroic actions.”

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Chief MacMillan says the Donohue family wishes to extend sincere condolences to the family of MIT police officer Sean Collier who was killed by the suspects earlier in the night.