Meanwhile, two U.S. officials said Dzhokhar Tsarnaev told interrogators that he and his brother initially considered setting off their bombs on July Fourth.
Boston police said they planned to review security procedures for the Independence Day Boston Pops concert and fireworks display, which draws a crowd of more than 500,000 annually and is broadcast to a national TV audience. Authorities plan to look at security procedures for large events held in other cities, notably the massive New Year's Eve celebration held each year in New York City's Times Square, Massachusetts state police spokesman David Procopio said.
Gov. Deval Patrick said everything possible will be done to assure a safe event.
"I think the most important thing is that we got them, and there's investigation continuing about where the other leads may lead," he said. "I can tell you, having been thoroughly briefed, that the law enforcement at every level is pursuing everything."
As part of the bombing investigation, federal, state and local authorities were searching the woods near the University of Massachusetts Dartmouth campus, where Dzhokhar Tsarnaev was a student. Christina DiIorio-Sterling, a spokeswoman for U.S. Attorney Carmen Ortiz, could not say what investigators were looking for but said residents should know there is no threat to public safety.
Dzhokhar Tsarnaev, who was found hiding in a tarp-covered boat in a suburban Boston backyard, faces a charge of using a weapon of mass destruction to kill. Three of his college classmates were arrested Wednesday and accused of helping after the bombing to remove a laptop and backpack from his dormitory room before the FBI searched it.
The April 15 bombing, using pressure cookers packed with explosives, nails, ball bearings and metal shards, killed three people and injured more than 260 others near the marathon's finish line.