23-Year-Old US Olympic Cyclist Kelly Catlin's Cause of Death Revealed

Kelly Catlin's cause of death was confirmed to be asphyxia by suicide, the Santa Clara Medical Examiner told E! News.

The 23-year-old U.S. Olympic track cyclist was found dead in her Stanford University campus residence on Friday. Kelly's father, Mark Catlin, confirmed her passing in a letter sent to VeloNews over the weekend, stating that she died by suicide.

"There isn't a minute that goes by that we don't think of her and think of the wonderful life she could have lived," Mark wrote in the letter. "There isn't a second in which we wouldn't freely give our lives in exchange for hers. The hurt is unbelievable."

"The U.S. cycling community suffered a devastating loss with the passing of Kelly Catlin, USA Cycling National Team member," Rob DeMartini, USA Cycling president and CEO, said in a statement. "Kelly was more than an athlete to us, and she will always be part of the USA Cycling family. Our thoughts and prayers are with the Catlin family. This is an incredibly difficult time and we want to respect their privacy."

A track cyclist and professional road cyclist, Catlin had been pursuing a graduate degree in Computational Mathematics at Stanford.

Catlin's sister, Christine, told PEOPLE that Catlin was struggling.

"On the phone she went back and forth from saying she was learning to appreciate things and enjoy life to saying if things didn't change in a month, she was probably still going to kill herself," Christine, 23, said. "This was only two weeks ago. I thought we had more time. My last words to her were, 'Please don't kill yourself.'"

Christine said Kelly's roommate found her and contacted authorities.

"When I heard the news I was biking and my mom called me," she recalled. "We had been worried because [Kelly] hadn't answered the phone in, like, a week. I was having a really sad feeling about that. When my mom called me I was hyperventilating and crying. I've been numb ever since."

The family said Kelly's mental health struggles began in December after she suffered a concussion during a race. She began having vision problems and headaches and was unable to complete workouts with the rest of her team, Mark said.

"My wife and I talked to her weekly on the phone and she started to express apathy about cycling, which she'd never done before," Mark says. "She had a lack of enthusiasm for the Olympic team, for training, for everything in life. We were concerned. She ran herself down. The concussion had a profound impact on her. She had these mental issues and she started to feel trapped."

After a failed attempt to die by suicide in January, Catlin underwent physical and mental health treatment for about two weeks before returning to school.

Kelly, who is one of a set of triplets, leaves behind her sister, Christine, and brother, Colin, and her parents, Mark Catlin and Carolyn Emory.

If you or someone you know needs help, please call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).