Boulder police believe a sexual assault over the weekend may be linked to another assault on the University of Colorado campus last week, and are now warning female students to be on alert.

Both attacks involved two men -- strangers to the victims -- and both attacks took place very early on a weekend morning and within several miles of each other.

Saturday's assault happened at about 3 a.m. along the Boulder Creek path. Police say two men attacked a 26-year-old woman when witnesses chased the suspects away.

A week prior, on Sunday at 1:30 a.m., a CU student was raped on campus near the Norlin library. In that case, one man knocked the victim to the ground and sexually assaulted her while another man acted as a lookout, the victim said.

Police have released a composite sketch of one suspect (pictured, left). He's described as a college-age, white male with red hair that's long in front, and short on the sides.

The second suspect was described as a white male, with dark hair who was shorter than 5 feet 6 inches tall.

The suspects are considered brazen and violent since the attacks took place in public.

"It's unusual and it's uncommon to have this type of sexual assault for a couple of reasons," said CU police spokesman Tim McGraw. "For one, it's a stranger rape. Those are very uncommon at CU, and in Boulder in general."

Police are hoping to obtain more forensic information from two baseball caps found at the scene of Saturday's sexual assault. One cap was black with an "A" on the bill. The other was blue and orange, with the "Miami Dolphins" emblem on the bill.

If you have any information on either of these cases, you are asked to call Boulder police.