Allison Bayliss, a 15 year-old sophomore of San Ramon Valley High School from Danville, who was reported missing since Monday afternoon is believed to have committed suicide.

Allison did not return from school on Monday afternoon, prompting her parents to call the police. On Tuesday, her father found her bicycle locked to a rack in the Battery East parking lot with her helmet in it, in the Presidio area of San Francisco, near the Golden Gate Bridge.

Police later found notes she had left on her computer where she researched BART schedules and airlines.

Allison left a suicide note, and notes to friends and family. It seemed like she determined to end her life at the Golden Gate Bridge. Authorities believe Allison boarded a BART train in Dublin, Monday morning, exited at the Embarcadero Station, where a BART security camera snapped a photo of her wheeling her bike through the exit gates. According to the California Highway Patrol, she was seen on the bridge at about 10 a.m. Monday and wasn't seen leaving it.

Officials announced that the search has switched from ground recovery to a water recovery operation in the area near the Golden Gate Bridge as it is now confirmed that Allison killed herself.

But there is no reason for Allison to commit suicide. She was a high-achiever at school. She held a 4.0 GPA, broke records as a swimmer and trained with other runners. She would always try her best at everything, her friends said.

Allison's friends described her as a quiet and friendly girl and a role model. Her friends recalled her as being generous, kind and optimistic.

She loved playing the piano and often posted videos of her instrumental pop song renditions on YouTube, her friends said.

Taylor Wood, 16, who had known Allison since middle school, said he thought she had gone somewhere alone to listen to music when he first heard of her disappearance. Music is what impacts all of us, he said. I thought she was by herself with her music, maybe because that's what I would have done.