The April 15 Patriot’s Day holiday in Boston found more than a few lawyers hard at work in offices scattered throughout the city’s Copley Square, notwithstanding the festival atmosphere attending the Boston Marathon outside. Some ended up trapped as authorities locked down the area after the two explosions, seconds apart, unleashed chaos at around 2:50 p.m. The recovery — and a massive criminal investigation — began immediately.

MONDAY

The Prudential Center and other nearby high-rise skyscrapers are home to a number of law firms, including Tarlow, Breed, Hart & Rodgers. Name partner Ed Tarlow said the building was locked down and "nobody can get in and out." Outside his window, near the end of the business day, he saw many armored and state trooper vehicles. "At one point there were 30 to 50 ambulances." Employees "are really shaken by the fact that it happened in the area."

TUESDAY

The investigation in full swing, President Obama addressed reporters following briefings by top officials including Attorney General Eric Holder Jr. and FBI Director Robert Mueller III. "[G]iven what we now know about what took place, the FBI is investigating it as an act of terrorism," Obama said. The FBI has "already begun conducting exhaustive interviews, analyzing evidence recovered from the scene and examining video footage for possible leads," Holder said.

A former prosecutor with counterterrorism experience predicted that overwhelming resources would be brought to bear. "I would bet the manpower associated with this investigation is incredible — and rightfully so," said Dan Collins of Drinker Biddle & Reath, who was lead prosecutor in the 2008 terrorist attacks in Mumbai, India, and a separate planned attack in Copenhagen, Denmark.

Robins, Kaplan, Miller & Ciresi of Minneapolis reopened its office in the Prudential Tower. "People are still on edge when they see Boylston Street completely deserted in front of our building," regional managing partner Tony Froio said. "It looks like a deserted movie set. It’s really eerie — really strange."

WEDNESDAY

Following a bomb scare that cleared Boston’s John Joseph Moakley federal courthouse for more than an hour, officials canceled a press briefing about the investigation but swatted down news reports that a suspect had been taken into custody. "No one has been arrested. No one is in custody," said Brandy Donini-Melanson, a spokeswoman for the U.S. attorney’s office. Authorities disclosed that video images taken at the scene contained images of a suspect, according to numerous reports. Officials were "very close" in the investigation, The Boston Globe reported.

THURSDAY

Richard DesLauriers, special agent-in-charge of the FBI’s Boston field office, released surveillance images of two suspects. Compensation guru Kenneth Feinberg, a native of Brockton, Mass., was tapped to administer The One Fund, established by Massachusetts Governor Deval Patrick and Boston Mayor Thomas Menino to coordinate assistance to victims. The Boston Bar Association rounded up lawyers willing to give pro bono advice to businesses harmed by the attack.

FRIDAY

A suspect now identified as Tamerlan Tsarnaev died following a shootout with police. Officers continued the hunt for his brother, Dzhokhar. Large swaths of Boston are placed under lockdown and the courts of law are closed. One consequence: postponement of a key hearing in the trial of Boston mobster James "Whitey" Bulger.