NEW DETAILS IN PETALUMA TEEN'S DEATH: CASA GRANDE GRAD LIKELY DISORIENTED, TOOK WRONG TURN AT TAHOE, OFFICIALS SAY

Alyssa Byrne, the 19-year-old from Petaluma found dead last week in South Lake Tahoe, apparently took a wrong turn New Year's Eve and wandered a short distance through snow before shedding her ski jacket and dying in the bitter cold on a snowbank, authorities said Monday.

Byrne was found dead three days later. Her boot prints -- the only ones in the vicinity -- suggested disorientation that may have been caused by alcohol consumption, hypothermia or both, El Dorado County Sheriff's Lt. Pete Van Arnum said.

"I don't want to speculate," he said, although he confirmed investigators had reports Byrne had been drinking while in town with friends for a music festival.

He noted advanced hypothermia causes confusion and deteriorating cognition. Victims can become disoriented and lose judgment.

"It was subzero that night and, depending on how long she was out in the cold, that could have affected her," Van Arnum said.

Experts say it's common for those with fatal hypothermia to remove clothing shortly before death because of physiological changes that cause a spreading sense of warmth.

The National Weather Service said it was minus 8 degrees overnight New Year's Eve in the area.

It's unclear when Byrne died. The Sacramento County Coroner's Office, which is handling the death investigation, has put the official date at Jan. 4, the day she was found. Authorities have said there were no signs of traumatic injury or foul play.

Douglas County, Nev., investigators, who led the initial search for Byrne, said she last used her cellphone at 11:53 p.m. New Year's Eve and was believed to have collapsed after leaving the final concert of a three-day music festival at Lake Tahoe Community College, a half-mile from where her body was found.

The 2011 Casa Grande High School graduate had driven Dec. 29 to Lake Tahoe with three friends with whom she attended the festival and shared a room at the Horizon Casino Resort in nearby Stateline, Nev.

But on New Year's Eve, she got ahead of her companions in a concert crowd and disappeared around 11 p.m., friend and former classmate Jay Donnellan said.

Byrne told Donnellan by phone at 11:23 p.m. that she was taking a shuttle bus back to the Horizon. He never saw her again.

For the next three days, family and friends conducted a frantic search for her.

Her body was spotted Friday morning by a public utility worker who was perched on a bucket truck and able to peer over a 4-foot-high snow bank that had hidden her from motorists and others.

Byrne was about 10 feet off Pioneer Trail, near Al Tahoe Boulevard, which leads to the junior college and runs between Pioneer Trail and Highway 50.

Authorities said long shuttle bus lines may have caused her to join others who decided to walk back to Stateline along an about four-mile route that would have followed Al Tahoe Boulevard and then turned to the northeast along Pioneer Trail. It also is possible she walked through the campus instead of taking a bike path used by others, Van Arnum said.

But her final location indicated she turned right on Pioneer Trail, rather then left as would be expected, and walked along the road before climbing the berm of frozen snow, Van Arnum said.

"Most of the people, if they were walking on foot and if they were headed back to the Stateline area, would have been going the other direction," he said.

Byrne's boot prints were visible coming over the berm and for about 100 yards along the back side of the snow bank, he said.

"It looked like she was kind of disoriented from the footprints. They kind of wandered a bit," he said.

Byrne was fully clothed when she died, except for her white ski jacket, which was found a short distance away, he said.

Investigators hope an autopsy scheduled today in Sacramento will shed some light on what happened. Toxicology tests may take a month, Van Arnum said.

Still unexplained is a report from a Petaluma friend, Micah Alex, who said he and his girlfriend talked with Byrne at the Horizon around 12:30 a.m. last Tuesday after all of them returned from SnowGlobe. By that point, he said, she appeared to be impaired by alcohol or drugs but he wasn't sure which.

Investigators have surveillance video that shows Alex at the hotel, but they had not found any footage of Byrne and believe he may have made a mistake about when he saw her.

But Donnellan said he is convinced that Byrne was on the bus when she told him she was and that Alex was right about seeing her back at the hotel.

When she left the festival, "she was functioning fine. She could hold a conversation. She seemed almost normal."

"... There's no way she would say 'I'm on the shuttle bus' when in reality she was walking," Donnellan said. "Micah saw her in the lobby. There's no other explanation. What happened after that, I have no idea."

Byrne's father, Kevin, said there will be a time for addressing the unanswered questions, including how a music festival that attracted many people younger than his daughter, might improve on its transportation system.

"My concern is I don't want to see this happen for another kid, another family," he said.

He said his mission now is to get through each hour with his family and to ensure all of the young people mourning his daughter have the support they need.

Byrne said each day since learning of his daughter's death has been harder than the last, making it a challenge to rise each morning.

But he said his wife, Kim, and son, Greg, have been amazingly strong, and all three have been buoyed by "an outpouring of support and love ... from the entire community."

Byrne said spending time with his daughter's friends has helped him cope, including Donnellan and Alex, whom he called "adopted sons."

"I have nothing but love for those kids," he said.

"It was just a bad situation" that resulted in his daughter's death, he said. "A perfect storm."

He said Casa Grande High staffers plan to box up artwork, messages and other mementos left at the school in memory of his daughter, and the school offered use of its gym for her public memorial, which will be at 10 a.m. Saturday.

Several local restaurants, including Beyond the Glory sports bar, his son's employer, have held fundraisers to help the family.

You can reach Staff Writer

Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com.