Jessica Moscatel came out as transgender in 11th-grade English class this spring. The teen asked classmates and teachers to call him Riley Matthew Moscatel from then on.
The request met little resistance at Bucks County Technical High School, which has other transgender or openly gay students.
"Everyone supported him," said a friend, Kate Cimino, who will be a junior this year. "Everyone loved Riley. He was everyone's best friend."
But on Monday, the 17-year-old appeared to commit suicide, the county Coroner's Office said. Police recovered surveillance video that showed the teen stepping in front of an Amtrak train near his home in Bristol Township.
Coroner Joseph Campbell said Wednesday that his office was continuing to investigate the death. Efforts to reach Moscatel's family were unsuccessful.
His friends and teachers were grasping for answers Wednesday. Friends said he had suffered from depression when he was younger but had improved. However, they said he felt increasingly uncomfortable in his female body.
A note Moscatel appeared to have posted on his Instagram account Monday stated: "My mirror reflects Jessica, my heart and mind say Riley ... You see me as the happiest person in school, I'm a prisoner of my own body ..."
Moscatel "still really wasn't a guy physically," Cimino said. "Even though everyone showed support and called him Riley, it didn't match up to what he felt of himself."
Another friend, Carley Foss, said: "He was super-frustrated with his body. And more and more frustrated every single day."
Foss said Moscatel had been researching hormone treatments, which he hoped to begin after he turned 18 this December. He also wanted to have breast surgery.
Rates of suicide and suicide attempts are much higher among transgender people - as much as 41 percent, according to one survey - compared with the rest of the population, experts say. But it's a complicated and understudied issue, particularly among youths.
Arnold Grossman, a New York University professor of applied psychology, is studying the issue with funds from the National Institute of Mental Health. He said suicide attempts by transgender youth often stem from feelings of not belonging, burdening family members, and seeing no way out of the situation.
Michele Angello, a psychotherapist based in Wayne, noted the sense of despair that can come from feeling disconnected from one's body. Other pressures for such young people include a lack of support, being bullied, and having trouble finding a job.
"I have amazingly intelligent and beautiful adolescents coming into my office in total despair because of one of those factors," she said.
The uncomfortableness for transgender youth can be intense enough to "throw them into crisis," said Andrew Spiers, co-coordinator of the trans health information project GALAEI, a Latino social justice organization in Philadelphia.
"Anybody that's transitioning should probably be seeing a therapist," Spiers said. "For teenagers, given what they're going through on top of questions about gender identity, that's a lot to handle."
Kevin Gentilcore, supervisor of Pupil Personnel Services at the tech school, said Moscatel's teachers were devastated.
"They said Riley had a great year last year," he said. "She felt supported by friends and family and that's why this has shocked everyone."
He described the school as one that accepts "all of our children for who they are and as they are."
"With all of our support and the school culture we have, if we have a student who chooses to take their own life, it can happen anywhere," he said.