A computer expert testifying in the Boston Marathon bombing trial says Dzhokhar Tsarnaev’s older brother did Internet searches on bombing components in the weeks before the 2013 terror attack.

The expert says search terms on Tamerlan Tsarnaev’s laptop included “detonator, “transmitter and receiver” and “fireworks firing system.” He says Dzhokhar Tsarnaev’s laptop showed his computer activity focused heavily on Facebook and a Russian version of Facebook.

The testimony is part of an effort by Tsarnaev’s lawyers to show that Tamerlan was the mastermind of the bombings. The defense admitted during opening statements that Dzhokhar participated in the attack but said he fell under the influence of the radicalized Tamerlan.

Tamerlan died following a shootout with police days after the bombings.

(AP)