A few hours before he was arrested in an FBI sting operation, a Queens man accused of trying to blow up New York's Federal Reserve building calmly spoke via Skype with his parents in Bangladesh and updated them on his studies.

They were stunned Thursday to find out that the banker's son from a middle-class neighborhood in Dhaka was accused of trying to carry out a terror attack.

"My son couldn't have done it," his distraught father, Quazi Ahsanullah, said.

"My brother may have been a victim of a conspiracy," said his sister, Fariel Bilkis.

The FBI arrested Quazi Mohammad Rezwanul Ahsan Nafis on Wednesday after he tried to detonate a fake 1,000-pound car bomb, according to a criminal complaint. Prosecutors said Nafis traveled to the United States on a student visa in January to carry out an attack.

Nafis' family said he went to America to study business administration, not to carry out an attack.

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"He is very gentle and devoted to his studies," his father said, pointing to Nafis' time studying at the private North South University in Dhaka, the capital.

However, Belal Ahmed, a spokesman for the university, said Nafis was a terrible student who was put on probation and threatened with expulsion if he didn't bring his grades up. Nafis eventually just stopped coming to school, Ahmed said.

Ahsanullah said his son persuaded him to send him to America to study, arguing that with a U.S. degree he had a better chance at success in Bangladesh.

"I spent all my savings to send him to America," he said.

Nafis attended Southeast Missouri State University during the spring semester, which ended in May, in pursuit of a bachelor's degree in cybersecurity.

He transferred this month to ASA College in New York, briefly attending the business and computer technology school's Manhattan campus.

Just a few hours before his arrest, Nafis talked to his mother over Skype to update her on his plans, Bilkis said.

"My brother told my mother that he was doing well in studies in the U.S. and was transferring to a college in New York," she said.

Nafis moved to Jamaica, Queens, where a taxi driver who lives in the same building remembered him Thursday as quiet and polite.

When he first saw Nafis, Mohammad Chowdhury, 45, asked his second-floor neighbor, Shamin Kahn, who that was.

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He said Kahn told him it was a relative. Kahn shares an apartment with his wife and their child, as well as Kahn's parents.

"He's quiet," Chowdhury said of Nafis. "He just says 'hi' and 'hello.' "

At the building, Chowdhury said he ran into Nafis three or four times, twice around 4 a.m.

"I didn't see anyone with him," he said.

With Chau Lam,

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Igor Kossov and AP