Fort Worth police are asking for the public’s help in finding an armed robber who has hit at least 14 businesses in recent weeks, including three just on Wednesday.

Spergel "Ray" Polk, 50, is suspected of committing the spree, police said.

Polk's criminal record dates to 1994. He was released from prison in April after a previous conviction for armed robbery, records show.

"This guy is extremely prolific," said robbery Detectve Brian Raynsford.

In his first alleged robberies, Polk presented a note demanding money and did not show a gun. But in his most recent alleged robberies he appears to be armed, Raynsford said.

Polk also appears to be getting more aggressive, police said.

In a pizza robbery about two weeks ago, police said he ripped the cash register off the counter when the clerk fled to the back, according to surveillance video.

And when robbing a pharmacy in East Fort Worth Monday night, he got in a scuffle with a store employee, police said.

Some of the most recent victims describe Polk as appearing very nervous and full of sweat.

"So there's some kind of stressor going on with him that's concerning us, that he's going to start escalating," Raynsford said. "So we need to get this guy in custody as soon as we can."

Polk should be considered armed and dangerous, police warned.

"We don't want any civilians to approach this individual or contact him,” Raynsford said. “Let the police do that. That's our job."