WATERTOWN, Mass. – Investigators have discovered that Boston bombing suspect Dzhokhar Tsarnaev scrawled a note inside the boat he was hiding in, claiming responsibility for the attacks on April 15 and saying they were retribution, several news organizations have reported.

The note reads as part manifesto, part suicide note and part justification for launching the deadly attack on civilians, CBS News senior correspondent John Miller reported Thursday.

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The note, written in marker on the interior wall of the cabin, said the bombings were payback for U.S. military action in Afghanistan and Iraq, and called the Boston victims “collateral damage” in the same way Muslims have been in the American-led wars.

When you attack one Muslim, you attack all Muslims,” Tsarnaev, 19, wrote, according to CBS.

Three people were killed and more than 260 were injured at the finish line of the Boston Marathon when two bombs exploded.

Tsarnaev’s older brother, Tamerlan, died in a shootout with police, after which an injured Dzhokhar hid in the boat in the yard of a house in Watertown.

Tsarnaev said he didn’t mourn Tamerlan, who was a martyr, and that Dzhokhar expected to join his brother in paradise soon.