"The video has changed the way we conduct investigations and has vastly improved our ability to identify suspects and solve crimes," said Paul MacMillan, Massachusetts Bay Transportation Authority Transit Police chief.

In a video released today by the MBTA, Brown's Chevy Malibu can be seen crossing the median line before slamming head-on into an MBTA bus in Holbrook.

It's compelling footage. But transit police also see it as an important tool.

"I'll tell you, there isn't a day that goes by that we don't use them," said Transit Police Sergeant Ken Sprague, of the cameras.

Approximately 350 buses of the MBTA fleet of 1,100 are equipped with eight cameras each, providing views inside the bus, in front, and on either side. Some MBTA subway cars and stations also have video cameras.

In incidents such as Monday's, video can help condemn some and vindicate others.

Sprague said the footage showed the bus driver was not at fault, and that Brown probably fell asleep. He said that Brown appears to be slumped down before impact. She was cited with failure to stay within marked lanes.

Brown could not be reached today for comment.

Surveillance footage from a bus also led to the arrest of five individuals this morning, each charged with assault by means of a dangerous weapon. Four had been filmed Sept. 9 brandishing knives on an MBTA bus in Boston.

The footage has also helped solve crimes not committed on MBTA buses. Transit police receive outside requests for footage nearly every day, MacMillan said.

"If the individual came on the MBTA after the crime, we may be able to identify them," he said. Plus, cameras pointing outwards on either side of buses can catch suspects walking on the sidewalk or accidents yards away, Sprague said.

The footage doesn't always show the darker side of human nature. Video from Monday's accident shows a man hopping off the bus within 15 seconds of the crash and rushing to help Brown. He helps her to the sidewalk and then calls police with his cellphone.

Brown, 54, of Whitman, was taken to South Shore Hospital in Weymouth with non-life-threatening injuries on Monday and remained there through tonight, a hospital official said. A 12-year-old female passenger on the bus was taken to Caritas Good Samaritan Medical Center in Brockton with minor injuries and later released, Sprague said.