Surviving Boston Marathon bombing suspect Dzhokhar Tsarnaev scrawled a note inside the hull of the boat where he was hiding from police explaining why he and his brother planned the attack.
Tsarnaev wrote that the bombings were in retaliation for American action against Muslims in Afghanistan and Iraq.
Tsarnaev and his older brother, Tamerlan Tsarnaev, are accused of planting two bombs that exploded near the marathon finish line on April 15. Three people were killed and 264 people were injured.
Dzhokhar Tsarnaev was found bleeding and hiding in a boat in a Boston suburb after a daylong manhunt that effectively shut down the city.
Tamerlan was killed in a police shootout.
Investigators said Dzhokhar Tsarnaev told them after his capture that he and his brother acted alone. Tsarnaev is currently in a federal prison hospital and has been charged with using a weapon of mass destruction.
He could face the death penalty.
Investigators are looking into a six-month trip the older brother took to Russia last year for clues into his radicalization.
Tamerlan Tsarnaev was buried last week at a Muslim cemetery in Virginia after cemeteries in Massachusetts refused the body.