Jonathan Adam Roldan, 23, was arrested on Friday at his residence in East L.A. He coached junior varsity volleyball at Esteban Torres High School and was also a campus aide at the school.
"It's hard because he was a good coach," said student Stephanie Juarez. "Girls feel uncomfortable now."
Authorities say the 15-year-old victim reported what happened to school officials on Friday. Investigators believe the relationship began in September and ended this month. Roldan is accused of having sex with the girl in his pickup truck.
"The incidents did not happen at the school; the incidents happened in his vehicle," said Los Angeles County Sheriff's Sgt. Richard Ruiz.
During the investigation, sheriff's detectives identified a second 15-year-old student who was inappropriately touched by the suspect.
He was charged with three felony counts each of unlawful sexual intercourse, oral copulation of a person under 16 and sexual penetration by a foreign object involving the first alleged victim. He was also charged with three misdemeanor counts of child molesting involving the second alleged victim. If convicted, he faces up to 10 years in state prison.
Roldan pleaded not guilty at his arraignment on Tuesday, but his attorney indicated a plea deal was in the offing.
"The police have already interviewed all of the witnesses, including the defendant. My client admitted to the officers his involvement. This is not a case where there is some controversy as to the facts. We'll all be putting our heads together to come up with the appropriate punishment," defense attorney George F. Bird Jr. said after the hearing.
A judge set Roldan's bail at $360,000, saying he abused his position of trust and authority. Twenty people came to court to support him, including family and friends.
Roldan's attorney says his client will be seeing a psychologist. Roldan's next court appearance has been scheduled for Jan. 13.
Detectives are seeking the public's help identifying any other possible victims. Roldan has worked at the school since 2011. LAUSD says he was placed on unpaid compulsory leave, and if he is convicted, he will be fired.
"The District takes these charges very seriously. Every precaution is taken throughout L.A. Unified to ensure the safety of students and staff," LAUSD said in a statement.
Parents were notified by phone over the weekend about an arrest and a letter was sent home Monday with students, according to the district.
Anyone with information was urged to call the L.A. Sheriff's Department Special Victims Unit at (877) 710-5273.