But before 18-year-old Galareka Harrison killed Mia Henderson, she wrote a fake note in which the victim purportedly admitted falsely accusing her roommate and "mentioned ending her own life," university police Officer Mario Leon wrote.
Harrison entered the room, left the note on her roommate's desk and then stabbed her "numerous times," according to Leon's probable cause statement, filed in Pima County Justice Court.
Police would not say what Harrison had been accused of stealing and would not release the police report her roommate filed Aug. 28.
Henderson, also 18, died Wednesday morning.
Both girls were residents of communities on the Navajo Indian Reservation and were freshmen at the university.
Harrison was ordered held under $50,000 bond Thursday by a Tucson City Court judge at an initial appearance. The judge entered a not guilty plea on her behalf.
Harrison's mother, Janice Harrison, watched her daughter's brief televised appearance at the Pima County Jail complex and said she was in shock.
"She never did anything wrong," she said. "She's a real nice person. She's never been away from home. She has no record of anything like this."
She added that her daughter also had been injured and said, "I think she was protecting herself ... It looks like she was trying to defend herself."
University police responding to an early-morning call Wednesday at a residence hall complex found the two women with unspecified injuries.
Both were taken to University Medical Center, where Henderson was pronounced dead.
Harrison has turned down all media interview requests, a jail spokesman said.