HOUSTON -- Houston police need help finding a group of robbers they describe as very violent, KPRC Local 2 reported Tuesday.

Surveillance video from a pawn shop robbery shows a flash of a yellow shirt. Seconds later, a door opens and an employee is slammed to the floor and tied up.

Investigators said they believe the group has hit two Houston pawn shops and won't stop. They're incredibly organized and shockingly violent, officials said.

Four men pretended to be customers at the InstaCash pawn shop on Long Point on March 13. When other customers left, the group pulled out guns.

"They were tied up with zip ties," said Sgt. Rich Nieto with Houston Police Robbery Division. "Some were threatened with guns to their heads. One victim was repeatedly pistol whipped."

Police said the group wanted into the store's safe.

Detectives said they think the same group robbed the EZ Pawn shop on Valentine's Day. Police said basically the same method of operation was used -- four men went into the store. This time, one of them had a Taser gun and the others had guns.

"They basically show very little regard for human life in actions and in words," said Nieto.

The EZ Pawn employees were tied up and one was shocked with a Taser gun while another was kicked in the face, police said. The thieves got into the safe and got away with the goods, officials said.

Detectives said that with this level of violence and organization, their next hit could be anywhere.

"It doesn't look like going to stop any time soon," said Nieto.

Anyone with information is asked to call Crime Stoppers at 713-222-TIPS.