BOSTON -- Investigators believe Boston Marathon bombing suspect Tamerlan Tsarnaev built pressure-cooker bombs while watching his 3-year-old daughter at his Cambridge apartment, and that his wife was out working when most of them were assembled, a federal law enforcement source said.

The FBI is continuing to meet several times per week with Tsarnaev's wife, Katherine Russell, 24, whom they are showing photographs and documents as part of their probe into the bombings, the source said.

Russell worked long hours away from home as a health aide, and it remains unclear whether she had any knowledge of her husband's bombmaking, the source said. Since the Cambridge home was raided after brothers Tamerlan and Dzhokhar Tsarnaev were identified as suspects, she has been living with her parents in Rhode Island.

A copy of the online al-Qaida magazine Inspire, along with other jihadist materials, was found on Russell's computer, which she may have shared with her husband, the source has said.

"Devices appear to have been built while he was at home with the child," the source said. Those included the two pressure-cooker bombs detonated April 15 at the Boston Marathon, killing three people and injuring more than 260 others.

Tamerlan Tsarnaev, 26, died in a gunfight with authorities April 19, a day after authorities released photos of the suspects.

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He did not hold a job at the time of the bombings and had recently turned away from his amateur boxing career as he became increasingly religious.

Neighbors said they recall seeing him occasionally walking around outside with his daughter.

"He was home with the baby, so you saw him with her now and then," said Angelica Wojciech, who lives in the same Cambridge apartment building as the couple. "She worked and he took care of the baby. He looked like any other dad doing that. Just normal."

Russell's lawyer has said she had no knowledge of the marathon bombs, but investigators are still examining what she knew about her husband's activities, and what she spoke with him about on the phone after the FBI released his picture, the source said.

Forensic tests by FBI explosives experts have detected residue from explosives in the bathtub and kitchen sink in the couple's apartment, the source said.

The results, according to the source, appear to corroborate Dzhokhar Tsarnaev's statements to federal investigators that the brothers built the bombs in the apartment.

He has told investigators that he and his older brother learned to make the pressure-cooker bombs from instructions in Inspire.

Meanwhile, lawyers for Robel Phillipos, 19, one of three arrested college friends of Dzhokhar Tsarnaev, filed court papers Saturday proclaiming his innocence and calling on a judge to release him from jail at a hearing scheduled Monday in federal court here.

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The lawyers argued Phillipos' presence on the University of Massachusetts Dartmouth campus on the day the other friends allegedly got rid of evidence from Dzhokhar Tsarnaev's dorm room was a coincidence and that it had been more than two months since he had spoken to the bombing suspect or the other two arrested men.