FORT COLLINS, Colo. -- Fort Collins Police are investigating whether a sexual assault early Thursday is connected to a series of sexual assaults and break-ins around the city.

A 23-year-old woman called police to report that a man broke into her garden-level apartment through an unlocked window while the she was sleeping. The attacker blindfolded her and forced her to perform a sexual act, according to police.

Because the woman was blindfolded, she did not see her attacker, police said.

Police have received three other reports of women who were assaulted by a man who entered through unlocked windows, blindfolded and sexually assaulted them since May. While there is no evidence the crimes are related, police are looking into the possibility due to similarities in the crimes.

Police said that all of the victims have been in their 20s and were home alone at the time of the attacks. In all of the attacks, the man has gained entry to garden-level apartments through unlocked windows, blindfolded the victims and forced them to perform a sex act. Police are not specifying what type of sexual act victims are being forced to perform. In addition, all the assaults have occurred between 3 a.m. and 5 a.m.

Although all the victims had roommates, none of their roommates were home when the assaults occurred. Investigators, however, said that they are not sure whether the women are being watched before the attacks.

To help narrow their focus, police are working with an ex-FBI profiler to identify the kind of man who might commit these crimes, said police spokeswoman Rita Davis.

Although investigators have received several leads, they have not been able to develop a suspect, Davis said.