In Cambridge, Massachusetts, FBI agents -- guns drawn -- walked down the street near the home where the Boston Marathon bombing suspects lived.
Emergency vehicles lined the street, roads were cordoned off, and a suspicious red vehicle was towed from the scene.
Mark Santos, 29, a doctorate student at the Massachusetts Institute of Technology, said it's still sinking in that the suspects, whom he didn't personally know, lived directly across Norfolk Street.
"We were that close," said Santos, who has lived there since September. "It's not something you expect."
His roommate, Diana Jorge, 26, said she's been confused ever since police ordered her out of her home.
"I'm a bit worried. I never thought that this could happen here in Boston," she said.
Many residents in the area awoke to federal agents with machine guns banging on their doors and the commands: "Get out! Get out!"
Despite the calls for evacuation, some residents sat on sidewalks near a perimeter of crime scene tape. Others defied the commands to stay indoors and gathered to gawk as state and federal officers -- some in camouflage, most in flak vests -- canvassed the neighborhood.
Four miles west, in the suburb of Watertown, many residents remained on lockdown, stuck in their homes after a car chase led the Boston Marathon suspects and a cadre of police into their neighborhood.
Chaos ensued just hours after authorities released images of the suspects.
It was about 10 p.m. -- close to bedtime for many people, if not past it -- when police received a report that a robbery was under way at a convenience store near the MIT campus in Cambridge.
The robbery was the first in a series of crimes that unfolded overnight and well into the next morning, putting the city, suburbs and one of the country's premier universities on lockdown at various points through the night. Residents were told to stay inside, away from windows, as city services came to a halt.
About 20 minutes after the robbery, an MIT police officer was fatally shot while responding to a disturbance at Vassar and Main streets, amid several of the school's research facilities.
MIT was quick to warn its students of the mayhem on its Twitter feed and emergency services website.
"Gunshots were reported near Building 32 (Stata) which is currently surrounded by responding agencies. The area is cordoned off. Please stay clear of area until further notice," the university posted, asking students to stay away from one of the university's busiest buildings.
Police arrived on the scene to find the campus police officer in his car with multiple gunshot wounds. They took him to Massachusetts General Hospital, but it was too late. Patrol officer Sean Collier, 26, of Somerville, who joined the force in January 2012, was pronounced dead. Police believe the bombing suspects were responsible for the shooting.
"Sean was one of these guys who really looked at police work as a calling," MIT Police Chief John DiFava said in a statement. "He was born to be a police officer."
Shortly after the shooting came another report of violence: Two men -- whom police now say were brothers living in Cambridge -- hijacked a vehicle at gunpoint in Cambridge, telling the driver that they were the marathon bombers, a law enforcement source told CNN's Joe Johns.
At some point, at a gas station on Memorial Drive along the Charles River, the driver escaped uninjured, Cambridge police reported.
Police, who were tracking the vehicle using its built-in GPS system, picked up the chase in Watertown, a town of 31,000 just west of Boston. The pursuit went into a residential neighborhood, with the suspects throwing explosives at the police, officers said.
"The suspects and police also exchanged gunfire in the area of Dexter and Laurel streets. During this pursuit, an (Massachusetts Bay Transportation Authority) Police officer was seriously injured and transported to the hospital," Boston police said in a release.
Richard H. Donohue Jr., 33, was shot and wounded in the incident, a transit police spokesman said. CNN affiliate WBZ reported he has been with the department for three years. He was taken to Mount Auburn Hospital, WBZ said. The officer's condition was not immediately known.
Ultimately, one bomber -- later identified as Tamerlan Tsarnaev, 26 -- got out of the car. Police shot him, and his brother ran over him as he drove away, according to the law enforcement source.
Tamerlan Tsarnaev was critically injured. He had bullet wounds and an injury from an explosion. He was wearing explosives and had an explosive trigger, a source told CNN. He later died, while authorities say his brother, Dzhokar Tsarnaev, 19, escaped.
After a hellish week in Boston, residents probably didn't need to be reminded that he was believed armed and dangerous.