Four robberies -- two of them armed -- took place in Howard County over the previous week.
Police believe the incidents, which occurred in Ellicott City, Columbia and Scaggsville, are unrelated.
"As far as we know, they're not related and they just happened to occur in the same time period," said Sgt. Gary L. Gardner, police spokesman.
The most recent armed robbery occurred early yesterday morning at an Ellicott City gas station in the 4700 block of Dorsey Hall Drive.
Police said a man armed with what appeared to be a sawed-off shotgun entered the Mobil station and demanded money from a cashier. The man fled with an undisclosed amount of cash.
The suspect is described as a slim, clean-shaven black male between 25 and 30.
Of the two robberies that occurred Sunday, the first was at 10:30 a.m. at the 7-Eleven convenience store at the Cherry Tree Shopping Center in Scaggsville.
Police said a man purchased a number of items and left the
store, returning a short while later to demand money.
Police said the man told a clerk he had a gun hidden in his waist
band and would kill her if she did not comply.
When the clerk opened the cash register, the man walked behind the counter, grabbing an undisclosed amount of money. He fled the store on foot.
Police describe the suspect as a 5-foot-4-inch black male in his 20s, with a mustache, wearing a white T-shirt and green camouflage pants.
Later on Sunday, a man with a knife forced employees at the Cosmetic Center at the 10000 block of U.S. 40 to open a safe.
The man entered the Ellicott City store at 5:25 p.m. and asked to see a store manager. The man followed a clerk to the back room and displayed a knife, ordering the workers to open the safe, police said.
The man took an undisclosed amount of cash from the store and fled the store. Police reported no injuries.
Police describe the suspect as a 5-foot-9 black male in his 20s, wearing a teal shirt, black jeans, gold-rimmed glasses and a blue baseball hat with an "X" in gold sequins.
On Friday night, a group of three men beat a 20-year-old Columbia man and stole money from his friend in the parking lot of a WaWa convenience store.
The victim was standing with his girlfriend and a male friend near pay phones at 11:30 p.m. at the WaWa at the 10700 block of Hickory Ridge Road in Columbia. Two cars pulled into the parking lot and three men exited the cars, police said.
They began harassing the 20-year-old victim, and one of the men punched him in the face, police said. As the victim tried to get into his car, others followed and kicked his passenger side window.
The men then approached the male friend, punched him in the face and stole his wallet. The men fled in the two cars, one a late-model, light-colored foreign car and the other, a used
maroon Pontiac or Oldsmobile.
The man who was punched received facial cuts and was treated and released from Howard County General Hospital.
Police describe all three suspects as 5-foot-6 to 6-foot-2 black males, 18 to 20 years old. One wore a denim jacket with white fur; the second had light skin and green eyes, while the third was dark-skinned and wore a gray Michael Jordan T-shirt and red shorts.