Before he was rounded up in a sweep of suspected Al Qaeda terrorists in Yemen, Sharif Mobley was a laborer at five nuclear plant complexes in Maryland, New Jersey and Pennsylvania.

Authorities are investigating whether he might have had any access to sensitive information that would have been useful to terrorists.

Edwin Lyman, a senior staff scientist with the Union of Concerned Scientists, a watchdog of the nuclear power industry, said the case raises questions about security at the nation's nuclear power plants — even though Mobley has not been linked to any wrongdoing at any of them.

Some of the information used to give temporary workers like Mobley clearance comes from other nuclear power companies and is sometimes incomplete, Lyman said.

"The real question is: Was there information that the NRC or utilities could have seen that would have led to his disqualification?" Lyman asked.

Meanwhile, a law enforcement official said Friday that the U.S. government was aware of Mobley's potential extremist ties before Yemeni officials arrested him, but did not provide a time frame or details about what exactly was known about him.

The official spoke on condition of anonymity to discuss an ongoing investigation.

The Nuclear Regulatory Commission said Friday that Mobley worked between 2002 and 2008 for contractors who did work at the Salem and Hope Creek plants in New Jersey; the Peach Bottom, Limerick and Three Mile Island facilities in Pennsylvania; and Calvert Cliffs in Maryland.

Officials at PSEG Nuclear, which runs the complex in New Jersey, say he carried supplies and worked on routine maintenance mostly during periodic refueling outages, when hundreds of contracted employees descend upon the plants.

The NRC says a laborer typically would not have access to security-related or sensitive information.

Officials also say he passed screenings before he could work at the plants. The NRC says the screenings include criminal history checks, drug testing, psychological assessments and identity verification. The background checks are to be performed by either the nuclear plant operators or their contracting companies.

The plants also run behavior observation programs in which employees are taught to recognize and report suspicious activities.

Steve Kerekes, a spokesman for the industry trade group the Nuclear Energy Institute, said the industry has to share information about problem workers.

"To the best of our knowledge, with the regard to this individual, there was nothing to suggest any kind of problem with him," Kerekes said. "Had there been, under the system that we have, we have a personnel database that's in place that lets all our companies across the industry know instantaneously if someone is for some reason denied access or flagged for some other kind of reason related to their behavior."

Kerekes also said that before regulations changed in early 2003, workers could gain temporary access to plants before their screening was complete. It's not clear whether Mobley had access before he was completely cleared.

Mike Drewniak, a spokesman for New Jersey Gov. Chris Christie, said Mobley was never reported to be acting improperly and was not believed to have been involved in any breaches at the New Jersey plants.

Mobley is a 26-year-old natural-born U.S. citizen who grew up in Buena, New Jersey, and later lived in Philadelphia and Newark, Delaware. A former neighbor said he moved to Yemen about two years ago, supposedly to learn Arabic and study Islam.

He was among 11 Al Qaeda suspects detained this month in a security sweep in Yemen's capital of San'a this month. He was taken to the hospital over the weekend after he complained of feeling ill. Yemeni officials said he snatched a gun from a security guard and fatally shot one guard and wounded another before being captured.

His parents have said he is not a terrorist.

A former friend said he believed Mobley was becoming radical before he moved to Yemen about two years ago.

Roman Castro, an Army veteran who did a tour in Iraq after he and Mobley graduated from high school together in 2002, said Mobley had only these words for him in a chance meeting four years ago: "Get the hell away from me, you Muslim killer!"