Hours after he didn’t arrive at school on Wednesday, a 17-year-old California boy was found fatally stabbed in a river bed having been allegedly murdered by a 16-year-old friend, PEOPLE confirms.

The body of Jeremy Sanchez was discovered about 4 p.m. Wednesday at the San Gabriel River Trail by two other boys who had been looking for him along with Sanchez’s father, according to a news release and news conference by the Los Angeles County Sheriff’s Department.

Authorities believe Sanchez was stabbed and killed at the river bed.

The case began earlier that day when Sanchez’s school called his father to report that he had failed to attend class, which was uncharacteristic, authorities said.

The father filed a missing-persons report and went looking for his son himself.

On Thursday, one of the two boys in that search was arrested on suspicion of murder in Sanchez’s death after authorities were tipped off about his possible involvement and subsequently searched the suspect’s home.

The boy has not been identified by name, though investigators have described him as a 16-year-old friend of Sanchez. The exact nature of their relationship was unclear, however. According to the L.A. Times, they were romantically involved.

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The suspect remains in juvenile custody, according to the LASD, which is investigating the homicide. It was unclear if the teen has entered a plea or retained an attorney who could comment on his behalf.

A murder weapon has not been found and a motive is still being probed. Additional information about the case was not immediately available.

“We’re continuing our investigation and trying to solidify the motive for why this young man wanted to kill his friend,” sheriff’s Lt. John Corina told reporters on Thursday.

Remembering the Victim as the Grieving Ask: ‘Why?’

“There’s a lot of why questions,” Sanchez’s godmother, Christina Amigon, told the Orange County Register. “Why did he kill him? Why did he do this to him?”

Sanchez, described by school district officials as “a popular student-athlete,” was a junior at South El Monte High School, outside L.A., at the time of his death.

He played on the baseball and football teams in addition to wrestling for the school.

“We are all still in shock over the death of our student. … El Monte Union High School District sends our prayers and support to his family during this extraordinarily difficult time,” Edward Zuniga, the district superintendent, said in a statement to PEOPLE.

“We are supporting our school community in any way possible and providing grief counselors to help students cope with this tragedy,” Zuniga said.

“When things were low, he could always make you laugh,” an unnamed classmate told the L.A. Times.

However, the paper reports that Sanchez had also faced bullying and a student at the school said something similar to the O.C. Register.

“Some people were giving him a hard time,” said teammate Luis Polino, noting that Sanchez had posted on social media last year that he was bisexual.

Sanchez’s relationship with the football team was fraught as a result, it appears.

The Register reports that he quit playing in the fall due to the feeling that “he was being judged by some of his teammates,” Polino said. He rejoined the team at a later point and “was probably going to be a starting safety, receiver and backup quarterback” this coming season, said the varsity coach, Fank Gallardo.

Sanchez’s school principal, Amy Avina, said in a statement that there were no reports of him being bullied. “To our knowledge, Jeremy was a much-beloved and confident young man who had great relationships with his peers,” she said.

“There’s a big sadness in school,” Gallardo told the Times. “You can see it.”