DENVER -- A Denver man accused in the brutal sexual assault of a 61-year old woman, who later died, was advised of the charges against him Monday.

Willie Trimble, 45, has been charged with sexual assault and felony murder.

Investigators said DNA tests link Trimble to the crime.

The victim, Judith Pyle, was working as an usher at the Pepsi Center and had ridden a bus home from work on Dec. 8.

She was assaulted in an alley near 35th Avenue and Clayton Street in northeast Denver.

"The attack left her traumatized," said the victim's friend, Mark Rands. "She was on the ground in the snow for 2 hours, in 3 degree weather."

"This is a horrible, unspeakable act no matter who it happened to," said the victim's son, Ronald Pyle. "That it happened to my mother just makes it worse."

Ronald was home cooking dinner on the night of the attack. When his mom failed to show, he assumed that she was staying at a friends house because of the snow storm.

"While I was sitting there waiting and cooking her food and wondering, she was just a block and a half away in the alley screaming for help."

A neighbor finally heard her cries and called police.

Pyle was taken to a hospital, but died from exposure.

"She worked hard all her life, trying to raise her son as a single mom," Rands said.

Ronald Pyle said he's grateful police have made an arrest. And he said he's grateful he got to spend time with his mom on her birthday and on Thanksgiving Day.

He said he's not looking forward to Christmas.

"I know that she would just want me to be strong and celebrate the holiday for what it's supposed to be celebrated for," Ronald said. "Not for Santa, but for the birth of Jesus Christ our Savior, whom she's with now."

Judith Pyle will be buried at 1:45 p.m. Friday, Dec. 28 at Crown Hill Cemetery.

Rand said friends are trying to raise money for a headstone.

Contributions are being accepted at: The Judith Pyle Memorial Fund, P.O. Box 291031, Denver, CO 80229-1031.