BOSTON (CBS/AP) – Boston Marathon bombings suspect Dzhokhar Tsarnaev has told investigators the U.S. wars in Iraq and Afghanistan motivated him and his brother to launch the attacks, according to a published report.

The Washington Post report Tuesday cited “U.S. officials familiar with the interviews.”

Tsarnaev, 19, is being held under heavy guard in fair condition at Beth Israel Deaconess Medical Center.

The Post also reported that Tsarnaev “has acknowledged his role in planting the explosives near the finish line on April 15.”

Tsarnaev was arrested last Friday, hours after his brother Tamerlan was killed in a shootout in Watertown.

Tamerlan Tsarnaev was an ardent reader of jihadist websites and extremist propaganda, U.S. officials told the Associated Press Tuesday, suggesting the brothers were motivated by an anti-American, radical version of Islam.

CBS News has learned that Tamerlan purchased two “lock and load” pyrotechnics in February from a fireworks store in New Hampshire. William Weimer, vice president of Phantom Fireworks, does not believe what was purchased was enough to be used in bombs.

Weimer told CBS News that each firework has 24 shells containing 60 grams of composition of powder, half of which is black powder.

Interrogators have been questioning Dzhokhar Tsarnaev at the hospital, letting him write down his replies, and his answers led them to believe he and his brother were motivated by religious extremism but appeared to have no major terrorist group connections, said U.S. officials, who spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.

However, the written communication precluded back-and-forth exchanges often crucial to establishing key facts, officials said. They warned that they were still trying to verify what Tsarnaev told them and were poring over his telephone and online communications.

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