Newly unsealed documents reveal that Boston Marathon bomber Dzhokhar Tsarnaev told FBI agents that he and his brother picked their own spots to place their bombs and that each of them set off his own device.

Tsarnaev talked to FBI agents at a hospital where was undergoing treatment for gunshot wounds. The interviewed him six days after the 2013 bombing, but a summary of his statements, prepared by the FBI, had not previously been disclosed.

Portions of it were made public Monday by lawyers for a friend of Tsarnaev’s, Robel Phillipos, convicted of lying to investigators after the bombing. Phillipos has claimed he did not know of the bombing plans.

According to the FBI summary, Tsarnaev told the agents he and his older brother, Tamerlan, walked toward the marathon finish line on the day of the bombing, April 15, each carrying a backpack containing a powerful bomb. He said he called his brother just before the attack to “synchronize the two detonations.” Tamerlan set off the first bomb, and Dzhokhar’s followed ten seconds later.