-- The eldest son of the 13 siblings allegedly held captive by his parents was allowed out of the house to attend a Southern California community college for years, where he had a GPA of 3.932, according to a transcript from December.
The 25-year-old's classes included music, algebra, English, guitar, basic auto mechanics and public speaking.
Several of his former classmates at Mt. San Jacinto College spoke to ABC News, including Josh Boldt, who described him as "really pale."
"It was kind of odd -- not something you see a lot of times, someone that's really pale. Really malnutritioned kind of looking," Boldt said. "He always this kind of depressive aura about him, if that makes sense, and he really, really kept to himself. ... He didn't really open up."
Louise Turpin, the 25-year-old's mother, would go with her son to the school and "wait outside the classroom for him. When he was finished with class, she would take him home," according to Riverside County District Attorney Mike Hestrin.
Student Joe Chermak said that in the spring of 2016, during the music department's student showcase, he saw another man whom he believed to be the 25-year-old's father, David Turpin, with several children in matching clothes.
"They seemed well-behaved. And also, like, they were all in uniforms, so at first I thought it was a group of kids coming from another school," Chermak said. "We didn't really think much of it, but all I know is that they left kind of abruptly in the middle of the show."
"I noticed that some of them were skinny," Chermak added. "One of them you could tell from their arm, they were really skinny."
Student Marci Duncker said that last year, as soon as class was over, "he'd leave. ... Didn't really talk to anybody."
"I'd try to say 'Hi' a few times, all he did was look," Duncker said.
"I didn't see him after about a month or so," she added. "I think he just stopped coming."
David and Louise Turpin, accused of abusing their children for years, were arrested after the victims were found Jan. 14 at their Perris home. One of the children -- a 17-year-old girl -- had climbed out of a window and called 911 for help, according to police.
The Turpins allegedly forced the children to shower only once a year, shackled them and beat them routinely, Hestrin said. The victims weren't released from their chains even to go to the bathroom, according to Hestrin. When found, they hadn't been to a doctor in over four years and had never been to a dentist, he added.
Besides the eldest son, the other children were "supposedly homeschooled," Hestrin said, but "the children lacked even basic knowledge of life. Many of the children didn’t know what a police officer was."
The siblings -- ages 2 to 29 -- have since been hospitalized.
All the victims except for the toddler were severely malnourished, Hestrin said, adding that the eldest victim -- a 29-year-old woman -- weighed only 82 pounds when rescued. He said another child, a 12-year-old, was the weight of an average 7-year-old.
David Turpin, 57, and Louise Turpin, 49, have each been charged with 12 counts of torture, 12 counts of false imprisonment, seven counts of abuse of a dependent adult and six counts of child abuse. David Turpin was also charged with one count of a lewd act on a child under the age of 14 by force, fear or duress. They have pleaded not guilty.
David Macher, a lawyer for David Turpin, told ABC News, "What we would like the public to know is that our clients are presumed to be innocent and that’s a very important presumption." He added, "We’re going to provide a vigorous defense."
Mt. San Jacinto College said in a statement that it is "aware that one of the children of the Perris couple accused of torture and child endangerment was previously enrolled at MSJC. To protect the privacy of the student and abide by the Family Educational Rights and Privacy Act, we cannot comment further about the student."
"These allegations are extremely disturbing," the school added. "We at Mt. San Jacinto College are deeply saddened and horrified to hear of the allegations involving these children. Our hearts go out to the victims. MSJC will follow this story and will provide appropriate support from our institution."
Anyone with information about the case can call the tip line at the Riverside District Attorney's Office at 888-934-KIDS.
ABC News' Robert Zepeda contributed to this report.