Gregg Zoroya

USA TODAY

The arrest of a D.C. transit officer on charges of trying to aid the Islamic State could raise concerns among U.S. police departments about radicalization within the ranks, especially given officers' ability to access potential targets.

"They would be trusted by other officers, especially if they're in uniform or have identification and would therefore get access to areas that average commuters would not," said Phil Schertzing, a retired inspector for the Michigan State Police. "And, of course, they're carrying weapons."

Authorities arrested Nicholas Young, a 13-year veteran of the Metro Transit Police Department in Washington, D.C., on Wednesday. He is charged with attempting to provide material support to the Islamic State. He is the first U.S. police officer to face a terror-related charge.

Metro police arrest underscores 'see something, say something'

Joshua Stueve, spokesman for the U.S. attorney for the Eastern District of Virginia, said Young posed no threat to the transit system. Court documents show Young directed his efforts at seeking to help the Islamic State overseas.

Still, the case illustrates the potential havoc a radicalized police officer could represent and raises questions about how law enforcement agents are vetted.

"You think about an airport or a subway system, the kind of damage that could be done with explosives and so on ... we're talking vulnerable targets," said Frederick Shenkman, a law enforcement expert and professor emeritus at the University of Florida.

Experts said police agencies typically screen new applicants by checking prior employment, doing a criminal records check and ascertaining the type of discharge received if they were in the military.

Metro police arrest illustrates terror threat to transit

Some agencies will assign someone to do a background investigation, interviewing people who knew or worked with the applicant. But such background investigations can be expensive and many smaller departments don't do them, Shenkman said.

"There are 18,000 police agencies in the United States and they have 800,000 officers," he said. "They average 12 to 14 officers each. They're closer to being like Andy in Mayberry (of the 1960s Andy Griffith Show) than they are to being the NYPD."

Dan Stessel, chief spokesman for Metro Transit, said all new police applicants undergo background checks, but he declined to provide any further details about how extensive those might be.

Once a police officer is hired, follow-up examinations are rare unless some kind of aberrant conduct occurs, said Schertzing, who is also an associate professor at the Michigan State University School of Justice. So spotting a radical change in beliefs could be difficult if a person is able to keep them hidden.

"If it's something you're not bringing to work, if it's something that there are not any complaints about from co-workers or from citizens that would lead to an internal affairs investigation, then it may not be as noticeable," Schertzing said.