BOULDER | Police have closed their investigation into whether several female students at the University of Colorado were drugged at parties because of a problem with blood samples taken from some of the alleged victims.

The Daily Camera reports six women reported they believed they were drugged Oct. 17 at parties at four different fraternities near the school’s campus in Boulder.

According to police reports released last week, three of the women were treated at Boulder Community Health’s Foothills Hospital and had blood samples taken as part of their treatment. Police later served a warrant for those samples but the testing laboratory said they contained a “gel clot activator” that interfered with the testing equipment.

Boulder Community Health says it hasn’t heard of its blood samples being rejected in police investigations before.

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