Walla Walla police are investigating another robbery -- the fourth since October -- at an area business.

It is not known if the suspect is responsible for all of the robberies, but Walla Walla police Officer Tim Bennett said the description of the suspects are similar.

This time, the suspect entered the Baskin Robbins, 2003 Isaacs St., at 5:45 p.m. Sunday, displayed a knife and demanded cash, Bennett said.

The suspect grabbed an undisclosed amount of cash from the register before running away. No one was hurt.

If the robberies are connected, Bennett said this is the first time the robber has displayed a knife.

Police still are investigating robberies at Tom's Southgate Chevron on Nov. 13, Los Tapatios Market on Nov. 3 and the Taj Food Mart on Oct. 26.

In those three robberies, the suspect displayed a gun before getting away with cash. The suspect also ran out of the stores but was seen riding away on a bicycle in the first two hold-ups.

Anyone with information on the robberies can call Walla Walla police at 509-527-1960.