The officer took up a position on the side and fired at Tamerlan and Dzhokhar.
The brothers tossed out five pipe bombs; two or three exploded.
After the final blast, a shroud of smoke covered the street and an armed Tamerlan ran toward police, shooting as he approached.
"He starts closing in on one of my officers, and they're literally about 10 feet away from each other, exchanging gunfire," Chief Deveau said. "Then, he runs out of ammunition."
Neighbor Kitzenberg gave a similar account: "He was running down the street, still engaging in gunfire. ... As he got closer to the officers, he was taken down.
An officer tackled the suspect. Two others joined in and tried to handcuff him.
All of a sudden, the black SUV roared down the street. "Get outta the way," an officer screamed. Police leaped to the side at the last second.
The younger brother slammed into Tamerlan, dragging him about 20 yards. "Ran over his brother," said Deveau.
A typical gunfight lasts about a minute, Deveau said. The one with the Tsnarnaev brothers lasted about 10 minutes, with more than 200 rounds fired and three bomb blasts.
A transit officer was badly wounded in the exchange. The Watertown police on scene immediately turned their attention to trying to save his life.
The black SUV with Dzhokhar behind the wheel managed to escape, with cops giving chase.
It was shortly past 1 in the morning.
A boat leads to the big break
Blood was found inside the Mercedes ditched on Spruce Street. More blood was discovered outside the SUV, an indication Dzhokhar was wounded.
That morning, authorities took the unprecedented measure of telling residents of greater Boston to stay indoors. Schools were closed. Restaurants shut for the day. One of the nation's largest cities became a ghost town, its streets clear of people and traffic.
In Watertown, the Massachusetts State Police, FBI, and local police conducted a door-to-door search of homes on about 20 streets. They came up empty handed.
By 6 p.m., authorities said they believed the suspect was still in the region but they lifted the order to stay inside.
After being cooped up all day, David Henneberry wanted to check on his boat -- his favorite toy, his "baby" -- named Slip Away II. He had noticed from his house that its cover had come slightly off.
It had irked him for much of the day. The winds had been unusually strong that day. Henneberry figured the winds had loosened the cover.
He climbed three steps up a ladder and saw "a good amount of blood," Henneberry told CNN-affiliate WCVB.