FORT BEND COUNTY, Texas -- One man is suspected to be responsible for a series of robberies in Fort Bend County, officials told KPRC Local 2 Monday.

In surveillance video, the robber can be heard threatening his victim. He told the clerk to hurry, and at one point, he started counting down from three.

Detectives said the man was making the clerk at Fresno Grocery on F.M. 521 open the register at about 8 a.m. Saturday when another employee walked up. There was yelling.  The register opened, the man grabbed the cash and took off, officials said.

"He's been armed with a knife in every one of the robberies," Chief Deputy Craig Brady said. "He typically holds it to the clerk's throat."

Fort Bend County deputies said they believe the same man robbed four convenience stores over the weekend.

In another video, deputies said he just wore a different hat.

Video shows him behind the counter at the Fresno Food Market on F.M. 521 at about 5:30 p.m. Saturday, with his arm around the clerk's neck. He goes for the cash drawer and when he turns to walk away, just how close the knife is to cutting her can be seen, deputies said.

As he's leaving the store, a customer enters. The man threw the clerk to the ground. She wasn't hurt, but said she is still traumatized.

Customers were in shock that the same man allegedly came into a Shell Station in the 7100 block of Highway 6 in Missouri City at about 9 p.m. Sunday armed with the knife -- only this time he really used it. The clerk was stabbed twice and had to be rushed to the hospital.

"He's a friendly guy. He didn't deserve that at all," said customer Kiana Parker.

"It seems he's getting more aggressive and more comfortable doing it, which is a scary thing," said customer Jake Land.

Detectives said they believe the same man is responsible for a robbery at the Valero station in the 2900 block of Texas Parkway at about 4:40 a.m. Saturday.

The man was described as white, about 6 feet tall with a slender build and brown hair and a mustache, He has been seen wearing a khaki shirt, blue jean shorts, sunglasses and different hats.

Anyone with information is asked to call Fort Bend County Crime Stoppers at 281-342-8477.