BOSTON – Bombing suspect Dzhokhar Tsarnaev and his older brother Tamerlan initially planned their attack for the upcoming July Fourth holiday but changed their minds shortly before the Boston Marathon because the race was an “ideal” target, a federal law enforcement source said Thursday.

The rapid assembly of two pressure cooker bombs that exploded at the marathon April 15 went faster than the two brothers expected and also weighed on their decision to change their plans, the source said.

Information about the switch in targets came from several investigative threads and details gleaned from hospital interviews with Dzhokhar Tsarnaev two weeks ago before he was read his Miranda rights and stopped talking to authorities, the source said.

The 19-year-old student at the University of Massachusetts Dartmouth told FBI agents he and Tamerlan Tsarnaev saw Patriots Day and the symbolism attached to it as an ideal time to set off the bombs, the source said. Turning the attack into a suicide bombing was one “possibility” the brothers considered, the source said.

Dzhokhar Tsarnaev told investigators that he and his brother built their pressure cooker bombs at Tamerlan Tsarnaev’s home, according to the source. Once they settled on a day for the attack, they scouted the marathon course before deciding that the finish line — packed with onlookers and a large news media presence — was where they would set off the bombs, the source said.

Federal investigators, meanwhile, continued to search two laptop computers belonging to the Tsarnaev brothers for any evidence the pair had help planning the attacks, according to the law enforcement source.

Tamerlan Tsarnaev’s computer, along with a laptop owned by Dzhokhar, were recovered in the days after the bombing. Investigators are poring over the two computers’ emails, pictures, contacts and any other data that could expand the probe, including whether Islamic leaders in Russia radicalized Tamerlan Tsarnaev, the source said.

Dzhokhar told investigators that he and his brother had listened to online sermons of Anwar al-Awlaki, the American-born radical who was killed in 2011 U.S. airstrike in Yemen, and an Islamic U.S. Army psychiatrist who allegedly shot and killed 13 and wounded 29 in 2009.

And also on Thursday, Tamerlan Tsarnaev’s body was claimed, said Terell Harris, a spokesman for the Boston medical examiner’s office.