A suspected Al Qaeda militant who was known as a "sweetheart" by classmates at his New Jersey high school is being investigated by the FBI after his arrest in the Middle East for allegedly trying to shoot his way out of a hospital in Yemen.

Federal sources confirmed that 26-year-old Sharif Mobley, of Buena, N.J., is in custody after a shooting rampage in a Yemeni hospital that killed one guard and injured another.

FBI spokesman Rich Wolf in Baltimore said the agency is looking into the case. Mobley was reportedly being held prisoner in the hospital and was caught after a chase following the shooting.

And a spokesman for a group of nuclear power plants in New Jersey said late Thursday that Mobley had previously worked as a laborer for several contractors at its three plants from 2002 to 2008 carrying supplies and doing maintenance work.

Mobley satisfied federal background checks as recently as 2008, PSEG Nuclear spokesman Joe Delmar Delmar said, adding that Mobley also worked at other plants in the region.

Classmates who graduated with Mobley from Buena Regional High School in 2002 expressed shock at both his suspected Al Qaeda ties and his deadly escape attempt in Yemen.

Dawn Bass said she was "shocked" to learn of the allegations, adding that Mobley had been known as a friendly "sweetheart" in high school.

"He was always showing off in the back of the classroom doing his karate moves and stuff," Bass told FoxNews.com. "But he was just a regular kid, he was always talking to everybody — he was not shy."

Mobley's mother, meanwhile, told WMGM-TV the accusations are false but did say that when she last spoke to her son in late January he was in Yemen. She said the FBI had visited her for questioning but insisted her son has never been in trouble and is a good Muslim.

Mobley's father, Charles, said the family was waiting for further information.

"We don't know nothing, we're trying to hear something," Charles Mobley told WMGM-TV.

The FBI declined to comment further on the case, but sources say federal investigators have an interest in Mobley and are waiting for more information to come out of Yemen.

A member of the Yemeni intelligence service confirmed Thursday that the man, originally described in statements as foreign, was a Somali-American. The official spoke on condition of anonymity because he was not authorized to talk to the media.

He was originally arrested as part of an earlier sweep against Al Qaeda, according to other security officials, and was in prison on charges of membership of the group. He complained of being ill and was admitted to the hospital, where was held under heavy guard while he was treated for around a week until his escape attempt, said a member of the security forces.

Officials say he snatched a gun from one security guard and shot him, then made his way down from his fifth-floor room to the ground floor. Witnesses say he then got into a shootout with hospital security guards, who pinned him down until a unit of the anti-terrorism police apprehended him.

The West has expressed concern about the growing Al Qaeda presence in Yemen.

Michael Brothman of Vineland, N.J., said he graduated with Mobley. He remembered Mobley boasting that he had a black belt in karate, being a fan of anime and being competitive in gym class. Mobley was also a member of his high school's wrestling team.

Campaign finance records show Mobley received $75 as an election day worker for Gov. Jon Corzine's campaign in 2005.

"I was kind of shocked when my friend called me about the news reports," Brothman said.

FoxNews.com's Joshua Rhett Miller and The Associated Press contributed to this report.