LAKELAND, Fla. -- A suspected serial robber tied up two employees Wednesday night at a Dollar General on County Road 540-A East near Lakeland Highlands Blvd.

Surveillance video captured the frightening moments. A man wearing a surgical mask is seen telling one of the clerks to lie down while he binds her legs with a zip tie. She watches helplessly as he apparently instructs the other clerk to fill a bag with cash.

The man never shows a gun, but detectives said he told the clerks he had one.

“We don't like people that rob,” Polk County Sheriff Grady Judd said. “We really don't like people that rob with a gun.”

The man ties up the second clerk and leaves them both on the floor.

He calmly rides off on a bike, which investigators think is a ruse.

“He only rides up and leaves on a bike, so people don't see his getaway car,” Judd said.

Those who work at nearby businesses are shaken by the experience.

“I'm shocked. This is a great area, and it seems very safe,” Alicia Johnson, who works nearby, said. “It startles me.”

Investigators said the man has robbed at least five other stores in Lakeland, Winter Haven and Hillsborough County.

He is described as a black male, 6 feet tall, 220 to 230 pounds.

This is the first time he's tied up the clerks, according to investigators, but it's also the only time he didn't show a gun. They're offering a $3,000 reward for information leading to his arrest.

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