( CNN ) -- A former Marine and suspected serial rapist pleaded not guilty this week to raping and murdering 19-year-old college student Brianna Denison . The family of Brianna Denison launched a Web site dedicated to her memory after her death in 2008 . James Biela , 27 , is charged with first-degree murder , kidnapping and sexual assault in the disappearance of Denison , who was last seen alive on her friend 's sofa in Reno , Nevada , January 20 , 2008 . The construction worker entered his plea in Washoe County District Court on Wednesday . Judge Robert Perry set a tentative trial date for February 22 , 2010 , according to online court records . Denison , a sophomore at Santa Barbara City College in California , was visiting friends in her hometown of Reno when she disappeared . Three weeks later , her body was found in a field near her friend 's home , partially covered with snow . An autopsy determined she had been sexually assaulted and strangled . A pair of panties that were not hers also were found near the body , in what police said was a `` calling card '' that helped them connect Biela not only to Denison , but also to another sexual assault . In a press conference after Biela 's arrest in December , police said they were able to connect the former Marine 's DNA with a sample on the panties . Police also found DNA matching Biela 's on the rear door of the off-campus house where Denison was staying with friends . The sample also matched DNA found at the scene of a December 16 sexual assault , police said . The victim , a student at the University of Nevada , was able to escape her attacker and describe him in detail , police say . Both crimes bear a striking resemblance to several other sexual assaults in the area , leading police to believe that Biela is a serial rapist . They are asking other possible victims to come forward . The case went unsolved for almost 10 months until an anonymous tip from a friend of Biela 's former girlfriend broke this cold case wide open , police said . Investigators had established that the killer was from the Reno area and had an unusual fetish of collecting one victim 's underwear and leaving it at the next victim 's crime scene . The tipster caught investigators ' attention by telling them that Biela 's former girlfriend had found two pairs of thong panties in his truck . Detectives immediately followed up on the tip and , with permission from the former girlfriend , took DNA samples from Biela 's 4-year-old son . Lab tests showed that the boy 's father -- Biela -- was almost certainly a match for the DNA found on the doorknob and at the crime scene , police said . The finding was confirmed when Biela was arrested and ordered to submit DNA samples . An overnight session at the crime lab confirmed the match , and charges were filed , police said . Investigators said they since have learned that Biela was familiar with the grounds of the university , having worked there on a construction job last year . Police say his work on campus put him in a position to easily target women . When first questioned about the Denison case in early November , Biela refused to submit DNA samples and provided an alibi to police , saying he 'd been with his girlfriend . The girlfriend denies that he was with her the night Denison disappeared , investigators said . Calls to Biela 's public defenders Friday were not answered . Meanwhile , investigators are certain there are other victims who have n't come forward . Police are urging anyone with more information to call the Reno Police Hot Line at 775-322-4900 . CNN 's Emanuella Grinberg and Rupa Mikkilineni contributed to this report .
James Michael Biela , 27 , is charged with murder of Brianna Denison , 19 . Police say the two had been dating for about a month and were planning to get married in August. Denison last seen on friend 's couch during visit to hometown of Reno , Nevada . Police say Biela left previous victim 's panties as `` calling card '' near Denison 's body .