Just hours after authorities released images of the suspects in the Boston Marathon bombings, the chaos ensued.
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 7-Eleven convenience store near the Massachusetts Institute of Technology 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. 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.
"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 and suspects in the marathon bombings -- had carjacked someone at gunpoint off Third Street in Cambridge, just blocks away.
Authorities say the men also kidnapped the driver, but only for 30 minutes or so. They dropped the victim off, uninjured, at a gas station on Memorial Drive, a thoroughfare running along the Charles River, Cambridge police reported.
Police located the car and gave chase into Watertown, a suburb of 31,000 just west of Boston.
"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," police said in a release.
CNN affiliate WBZ identified the transit officer as Richard Donohue Jr., 33, who had been with the department for three years. He was taken to Mount Auburn Hospital and was in critical condition, WBZ said.
Warnings to Watertown residents followed. First, Boston police tweeted, "There is an active incident ongoing in Watertown. Residents in that area are advised to remain in their homes. More details when available."
Then, a warning by state police that the search was intensifying: "Police will be going door by door, street by street, in and around Watertown. Police will be clearly identified. It is a fluid situation."
Police were chasing the suspects in Watertown, and explosives were hurled at officers during the pursuit.
One of the suspects, Tamerlan Tsarnaev, 26, 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.
Officers locked down the streets of a Watertown neighborhood -- the intersection of Dexter and Laurel streets lies in a heavily residential area -- after isolating the vehicle. SWAT members arrived on the scene, and police in full body armor carrying assault rifles ran down the streets, according to CNN affiliate WCVB.
Homeland Security Investigations agents were among those on the scene, a department spokesman said.
Police requested that residents in the area turn off their mobile phones, saying they believe the devices were used to detonate the Boston Marathon explosives. They went door to door, leaving an already-on-edge suburb even more anxious.
Back in Cambridge, police blocked the street and converged on another home, telling residents near Norfolk Street, "Ongoing investigation. Potentially dangerous. Stay clear."
Chris Howes, who asked local police via Twitter whether they had any advice for residents who lived on Norfolk, also wrote on Twitter, "This is scary as f***." Asked via Twitter whether he could provide more information, he tweeted, "don't really have any info. CPD told us to stay indoors so we just hear lots of sirens outside."
As news emerged that the suspects lived with their parents in the Norfolk Street area, nearby resident Amy McConnell tweeted, "Just so weird to think those guys have been walking around my neighborhood all week." She also declined