NEW YORK (CNN) -- Seven months have passed since the disappearance and slaying of college student Brianna Denison.
Brianna Denison, 19, disappeared when she was visiting friends at the University of Nevada, Reno.
The 19-year-old undergraduate from Santa Barbara, California, disappeared while visiting friends at the University of Nevada, Reno.
She was last seen sleeping on the living room sofa near an unlocked glass door of a friend's off-campus apartment after a night of partying.
Her friends awoke the next morning to find Denison missing, a small blood stain on her pillow. Her shoes, purse and cell phone were left behind.
Three weeks later, her body was found partially covered in snow in a nearby field. She'd been sexually assaulted and strangled.
But the killer left an unusual "calling card." According to authorities, he has a fetish for women's lingerie and makes it a habit to take the panties of his victims, leaving behind the previous victim's.
Along with Denison's remains, a pair of black thong panties was found. The panties did not belong to the victim and contained DNA from another, unidentified female.
Police are asking any woman who has lost a pair of black thong panties, size small, with a Pink Panther cartoon and heart design, to come forward.
Police have also been able to connect DNA found at the crime scene to a prior sexual assault that occurred December 16 and involved another university student. She managed to escape her attacker and described him in more detail to authorities. Watch how a serial rapist is stalking a college town »
Additionally, both crimes bear striking similarity to several other sexual assaults in the area, leading police to conclude that Denison's killer is a serial rapist who most likely lives or works in the area. The attacks all took place in close proximity to each other, during similar times of day and used similar methods.
In one of the earlier attacks, a university student was walking across a parking lot to her car when a man approached her from behind and put her in a choke hold. He pushed her to the ground and groped her. She fought him off and screamed. He kicked her in the head and then ran, dropping a couple of unopened condom packets.
In another incident, a student was attacked as she was parking her car outside her home. The assailant tried to choke her and force her inside his vehicle. He then drove her a few minutes away to a secluded area and sexually assaulted her, then beat her and drove her back to her residence.
He threatened that "he'd be back" if she told anyone. Victims describe the assailant as a white male, 28 to 40 years old, square chin, brown hair, about 5-foot-6, strong but not muscular, a small pot belly and short beard.
The vehicle associated with him is a small truck with an extended cab, automatic transmission and front bucket style seats with velour upholstery. One witness also describes seeing a baby shoe lying on the floorboard in the front passenger side of the truck.
Police and family are asking for the public's help in bringing Brianna Denison's killer to justice.
Please call the the Reno Police Hot Line at 775-745-3521 or the Secret Witness Line at 775-322-4900. Secret Witness is offering a $2,500 reward for anonymous tips that lead to an arrest and prosecution.