NEW YORK -- Jose Pimentel appears to have spent much of his time on the stoop of an upper Manhattan apartment building, smoking cigarettes and appearing to be such a layabout that one old schoolmate assumed he was a drug addict or homeless.

Police arrested the 27-year-old convert to Islam on Saturday and accused him of plotting to blow up U.S. targets -- including American soldiers returning from the wars in Iraq and Afghanistan -- and launch a one-man holy war in New York City. On Monday, Pimentel's mother, Carmen Sosa, seemed stunned by her son's arrest and unable to understand how he could have turned into a radical Muslim.

"I didn't raise him that way," Sosa, 56, told reporters who crowded into the hallway of the apartment building where Pimentel had been living with Sosa's brother.

"I want to apologize to the city. I love the city," said Sosa, who works at a nonprofit organization that helps find housing for the mentally ill. "I'm very disappointed with what my son was doing."

There were varied accounts of the family's recent history. New York police spokesman Paul Browne said Pimentel had converted to Islam in 2004 or 2005, while living in Schenectady, N.Y. "I'm not clear what drew him to Islam," Browne said.

The FBI was noticeably absent from the raid that led to Pimentel's arrest, and there were indications that federal officials were not convinced he was a serious threat.