Ames, Ia. — Tristan Adams was in Campustown Monday morning to help a friend who needed a job. What he found was a teenage girl who needed to be rescued.

Adams, 44, said he saw a girl, who Ames police say was kidnapped and raped, climb out of a second-story window. She was naked and crying, with blood in her mouth, screaming for help, Adams said Tuesday. When he realized a man was behind the girl, he shouted out that he was a police officer.

"She was leaping out the window, butt-naked," Adams said. "I saw there was a guy directly behind her who tried grabbing her with one hand."

Moments later, police arrested Michael Vincent Schweiger, 21, of 207 Lynn Ave. Officers chased Schweiger on foot, apprehending him about 9 a.m. about a tenth of a mile away outside a Campustown bookstore at 2300 Lincoln Way.

Schweiger, who police say was armed with a hatchet and a knife, was charged with first-degree kidnapping and second-degree sexual assault of a woman under the age of 18, said Cmdr. Randy Kessel of the Ames Police Department.

Schweiger sexually assaulted the teen repeatedly throughout the early morning hours Monday after threatening her with a knife, according to court papers.

Adams said he climbed onto the roof when he saw the man grabbing the teen. Police confirmed Adams was at the scene. Lt. Geoff Huff said Tuesday that he could not comment on this specific incident, but as a general rule citizens should not identify themselves as police officers.

Schweiger went back into the second-floor apartment, in a two-story, cream-colored house in the Campustown neighborhood. After Schweiger fled, Adams was able to reach the girl, he said.

"She grabbed hold of me," he said, adding that he told the girl she saved her own life by leaping out of the window.

Green extension cords were wrapped tightly to bind her arms and legs together, he said. The teen told him she was a 15-year-old runaway, Adams said. Adams said the girl had told him Schweiger "flipped" after she had told him she was pregnant.

The teen did not have any wounds from the weapons found on Schweiger, but police said she was very much at risk.

"I haven't seen anything of this magnitude in recent recollection," Kessel said of the crime.

The teen was taken to Mary Greeley Medical Center in Ames for treatment for the assault, police said.

She had been living for the past two weeks with Schweiger, who is not listed as an Iowa State University student, Kessel said.

The Des Moines Register's policy is to withhold the identity of alleged victims of sexual assault unless they agree to be named or file a lawsuit.

Schweiger is in custody at the Story County jail on a $932,500 cash-only bond.