A third Rapid City casino has been robbed in less than a week -- and the weapons used are getting bigger.

The Happy Jacks casino on Cambell Street was robbed early Thursday morning by a person with a sword, a day after two men with knives stole cash from a Happy Jacks on Mount Rushmore Road.

The parent company of Happy Jacks, M.G. Oil, is offering a $10,000 reward for "information leading to the arrest and the conviction of the robbers," vice president Troy Erickson said.

The Thursday robbery took place at 1:35 a.m. An individual described as about 5 feet, 5 inches tall, wearing black "ninja-type" clothing and a mask, walked in armed with a sword and demanded money. The clerk cooperated with the robber, who fled with an undisclosed amount of money.

The employee, who was the only person in the store during the incident, is "pretty shook up," Erickson said.

Erickson said he believes the three robberies -- including an armed robbery of Joker's Casino on Mount Rushmore Road on Sunday morning -- are connected.

Police released surveillance video of the first two robberies and hope the video will help catch the suspects. One of the robbers has a distinct limp.