The doors to a Center City bank swung open yesterday morning, and in shuffled trouble.

It's likely that at first, no one was intimidated by the presence of the man with the hunched shoulders, flat-brimmed baseball cap and large, dark sunglasses.

But within seconds, the awful truth was apparent inside the Citizens Bank at 20th and Market streets: They were in the presence of the rarest of criminals - an elderly bandit.

The thief, a white man who FBI officials said is "in his 60s, maybe 70s," struck at 9:34 a.m., when he handed a pillowcase to a bank teller and demanded cash.

The teller complied. FBI officials said the bandit fled on foot, and soon sported the fruits of his labor across his brown shirt - stains from an exploding dye pack that was hidden inside his stolen loot.

Surveillance images were released also showing the thin, 5-foot-11 crook - who wore khaki pants and brown, Timberland-style boots - as he entered the bank and then collected his pillowcase full of cash.

"Clearly, this was unusual," said an FBI spokesman, Special Agent J.J. Klaver. "He was on the older side of what we usually see."

Since 2006, the FBI has arrested just one bank robber who was in his 60s or 70s.

Typically, FBI agents are hunting for thieves who are in their 30s, Klaver noted.

Regardless of the culprits' ages, bank robberies are up in the city, with 50 so far this year compared with 44 at this point last year.

Despite a common theory that the economy may be nudging otherwise law-abiding citizens toward bank robbery, Klaver said that FBI agents have encountered few examples of criminals who have turned to robbing banks to pay the bills.

Klaver said that the aged thief didn't produce a handgun or a threatening note, contrary to early reports.

"He made a verbal demand, and then produced a pillowcase that he had hidden under his shirt," he added.

Tipsters can contact the FBI at 215-418-4000. *