Boulder police issued a warning to residents Wednesday after a third armed robbery involving a man with similar characteristics to the first two robberies.Police said a 40-year-old woman returning home a little after 11 p.m. Tuesday told officers that she had been robbed at gunpoint as she was gathering items out of her car in a parking garage at 2301 Pearl Street. She said she noticed a man riding a bike through the parking garage.The woman said she was collecting her purse and other items from her trunk when she saw the man on the bicycle circle back around and point a handgun at her. The man asked what she was carrying and the woman asked the gunman not to hurt her, according to police.The woman told police the man lifted the bottom of her dress to view her underwear and then grabbed her wrist and placed her hand on his groin, police said.The woman said someone made a noise in the garage which startled the man, and he fled on foot.The woman described the gunman as Hispanic and in his 20s. He had a round face, was about 5 feet 6 inches tall, had short, "spiky" hair and was wearing blue jeans. His shirt was not described."This is the third armed robbery involving a similar suspect description in Boulder since Thursday, and police are reminding residents to be alert to their surroundings," a news release stated.A similar armed robbery took place around 4 p.m. Monday in the 500 block of Canyon, along the Boulder Creek Bike Path. Three women were robbed of their purses at gunpoint by a Hispanic male, who fled eastbound on the path on a silver bike, authorities said.In that incident, the robber's gun discharged as he jumped on his bike to flee, but the man wasn't firing at the women and it may have been an accidental discharge, Boulder police spokeswoman Kim Kobel said earlier.On Thursday, a Hispanic suspect armed with a handgun robbed a female student on the University of Colorado campus. The victim was not injured."The information we have indicated they are related," Chief Mark Beckner told reporters Wednesday. "We can never be sure until we solve it, but we are currently operating under the premise that they are probably related."The robberies have some residents on alert."I'm going to make sure my doors are definitely locked. Be a lot more cautious, when I get into and out my car at night, said Boulder resident Marinela Simon.Anyone with information on any of the crimes is asked to contact the Boulder Police Department's tip line at 303-441-1974. Those who have information but wish to remain anonymous can contact the Northern Colorado Crime Stoppers at 1-800-222-TIPS (8477) or 1-800-444-3776. Tips can also be submitted through the Crime Stoppers website at www.crimeshurt.com.Those submitting tips through Crime Stoppers that lead to the arrest and filing of charges on a suspect(s) may be eligible for a cash reward of up to $1,000 from Crime Stoppers.