FORT COLLINS, Colo. -- Police are following up on dozens of tips they have received since a sixth sexual assault was reported last week.

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Julie Hayden Reports On The Investigation Rita Davis Discusses Latest Attack Residents On Guard After Sex Assault

Police believe the latest attack, reported Thursday morning, was linked to five others in a series of attacks that began in May. All six attacks targeted women in their 20s in apartments.

Police say the assailant entered through unlocked doors and windows, blindfolded the women and forced them to perform a sexual act. There was one attack in May, two in June, one in July and one Aug. 5.

An 11-member task force has been assigned to the case full-time, police spokeswoman Rita Davis said. Police have received more than 50 tips since the latest attack, police Lt. Dave Freismuth said.

"There are tips coming in constantly," he said. "The more the better."

Police have received more than 400 tips since May, Davis said.

Thursday's attack came as 23,000 students returned to Fort Collins for the start of classes at Colorado State University last week. Police distributed fliers to businesses carrying details of the assault and the suspect's description. A $10,000 reward has been posted for information leading to a conviction.

On Thursday, someone removed a window screen and entered the apartment of a 21-year-old woman and her 22-year-old roommate, both students at Front Range Community College.

Police said the man forced one woman to perform a sexual act and then went into the roommate's bedroom. The assailant was scared away when the first woman followed him into the second bedroom.