The pressure-cooker bombs used in the 2013 Boston Marathon attack were "not too difficult" to build, using readily available parts and instructions easily found on the Internet, an FBI bomb expert testified Thursday.

Edward Knapp, a supervisory special agent with the FBI, identified photos of various bomb components found at the scene of the attacks, including hobby fuse, a toggle switch, small Christmas tree bulbs and electronic speed controllers from remote-controlled cars.

Knapp said the bombs were made out of parts that are easy to find. He read aloud for the jury instructions on how to build pressure-cooker bombs as explained in Inspire magazine, an al-Qaida publication found on bomber Dzhokhar Tsarnaev's computer.

"It's not too difficult of a system to build," Knapp said.

Tsarnaev's lawyers have admitted that he and his late brother, Tamerlan, 26, detonated the bombs near the finish line April 15, 2013. But the defense says Tamerlan Tsarnaev was the mastermind of the attack and enlisted his then-19-year-old brother to help him in the months before the bombings.

Three people were killed and more than 260 were injured. Dzhokhar Tsarnaev faces the possibility of the death penalty.

Knapp also described a third pressure-cooker bomb thrown at police during a shootout in the Boston suburb of Watertown four days after the bombings. He said that bomb had a "dead man's switch" that could detonate the explosive if the operator is killed or incapacitated.

"A suicide bomber would have this type of configuration," Knapp said.

Prosecutors were expected to rest their case Monday in the first phase of the trial, known as the guilt phase. The same jury will hear evidence in a second phase of the trial to decide whether the 21-year-old Tsarnaev is sentenced to death or to life in prison.