As police and federal agents pursued him in a Boston suburb four days after the marathon bombings, Dzhokhar Tsarnaev left a “deathbed” note scrawled inside the hull of the boat where he was hiding that said the attack was retribution for wars the United States waged in Iraq and Afghanistan, according to two law enforcement officials.

The note — which one official said stated that if you attack one Muslim, you attack all Muslims — could serve as important evidence against Tsarnaev, the younger brother of Tamerlan Tsarnaev, a onetime boxer who is considered the mastermind behind the bombings. Some of Dzhokhar Tsarnaev’s friends have said they believed the older brother, who never assimilated to life in the United States, must have cajoled or brainwashed Dzhokhar into participating in the bombings.

The older Tsarnaev was killed days after the bombing, and his younger brother was captured in Watertown, Mass. Later, in his hospital room, he was questioned extensively by law enforcement about whether other potential threats existed, all without having his Miranda rights read to him.

But unlike those statements, the note scrawled with a pen inside the boat may constitute a plainly admissible statement of Tsarnaev’s motivation for his alleged participation in the April 15 attack near the finish line of the Boston Marathon.