An autopsy conducted on a Petaluma teen who died in South Lake Tahoe last week turned up no sign of injury or trauma, a law enforcement official said Wednesday.

Investigators must now await results from tests on tissue and blood samples to see if they yield additional clues about what led to the death of Alyssa Byrne, 19, on New Year's Eve, El Dorado County Sheriff's Lt. Pete Van Arnum said.

"They did extensive examinations, you know, for everything that could be a possibility, and they haven't found anything suspicious at this point," he said.

The test results, which likely will not be available for around four weeks, may furnish information about the role of hypothermia or any alcohol or drugs Byrne may have ingested, Van Arnum said.

Temperatures in the area dropped to minus 8 degrees Fahrenheit overnight New Year's Eve and early New Year's Day, when Byrne disappeared while attending an outdoor music festival with friends.

Byrne, who graduated from Casa Grande High School in 2011 and was attending Santa Rosa Junior College in hopes of becoming a firefighter/paramedic, was found frozen in the snow three days later, about a half-mile from the music venue at Lake Tahoe Community College.

Authorities believe she may have elected, like many other concert- goers, to avoid long shuttle-bus lines and walk back to the Stateline, Nev., hotel area where Byrne was sharing a room with three friends at the Horizon Casino Resort.

But where most would have taken a left turn onto Pioneer Trail from the college, Byrne's location suggested she turned right, away from town, Van Arnum said.

Her boot prints show where she left Pioneer Trail, climbed over a 4-foot bank of snow that had been plowed off the road, shed her ski jacket and wandered about 100 yards before coming to rest at the point where she was found, Van Arnum said.

The footprints suggest disorientation that could have resulted from advanced hypothermia, or perhaps from intoxication, authorities said.

Friends said Byrne had been drinking, but hypothermia also produces cognitive dysfunction and confusion, as well as metabolic changes that create a feeling of warmth, sometimes causing those with fatal hypothermia to remove clothing in the moments before death.

Authorities recovered Byrne's cellphone, which will be examined closely, Van Arnum said.

Authorities previously have said she last used it at 11:53 p.m. on New Year's Eve, a half-hour after she called a companion to tell him she was taking the shuttle bus back to their hotel.

That friend and others who called and texted her in the ensuing hours said she never responded.

Detectives from numerous law enforcement agencies are continuing their investigation into the circumstances of her death, in part to determine if it's possible to resolve questions raised by a friend who reported seeing her at the hotel after leaving the music festival.

Micah Alex said he and his girlfriend talked briefly with Byrne around 12:30 a.m. Jan. 1, and surveillance tape from the Horizon Casino Resort shows him with friends at the hotel, beginning around 12:05 a.m., Douglas County Sheriff's Sgt. Pat Brooks said. Alex was in the hotel for less than an hour, Brooks said. No image of Byrne has been found during that time frame.

A public memorial service open to anyone who wants to remember and honor Byrne is being held at 10 a.m. Saturday in the gymnasium at Casa Grande High.

Those attending are encouraged to wear pink, Byrne's favorite color.

You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com.