The straight-A student, who went to a community college in California, did not draw attention to himself, according to reports in his US homeland.
The eldest child, who has not yet been named for legal reasons but is 26-years-old, attended local community college Mt. San Jacinto College, according to the president’s honour roll.
ABC News obtained a transcript which showed he attended college between 2014 and 2016 and earned A grades in several classes, including algebra, guitar, public speaking, English fundamentals and freshman composition.
Former classmate Marci Duncker said the sibling had “one of the most sad faces” and that he was “always quiet and alone”.
She told ABC News: “I think he was in theory class last year.
“I don’t remember him being in any other classes but I do remember hearing his name and I do remember seeing him once, and I didn’t see him after about a month or so.
“I don’t think he ever dropped a class, I think he just stopped coming.
“He was kinda quiet. If I remember right I think he was hiding in a corner. Not hiding hiding, just off by himself. I just remember he would come and go. As soon as the class would leave he’d leave.
“He didn’t really talk to anybody. Wouldn’t really want to talk to anybody.
“I tried to say hi a few times, all he would do is look.
“I just thought it was strange, he was so quiet. Even those who are quiet will at least talk to people.”
Another classmate, Josh Boldt, said: “What I remember about him was he was really pale and kinda odd.
“It’s not something you see a lot someone who is really pale. [He was] really malnutrition kinda looking.
“On top of that he always had this kind of depressive aura about him, if that makes sense.
“And he really kept to himself. I feel bad that he was never able to speak out.
“He was really enclosed, a lot of us would open up pretty fast.”
Speaking of the eldest son’s behaviour while at college, Gale Kelley, a trainer for the International Association of Trauma Professionals, said his reluctance to report his parents was understandable.
She said: “They were born into this. This was normal for them. Some of them may not even realise they’ve been abused.
“These children have been living in isolation so they only know what they know.”
The student did not confess information about his parents David and Louise Turpin, aged 57 and 49, who have been charged 12 counts of torture, 12 of false imprisonment, six of child abuse and six of abuse of a dependant adult.
The parents deny all charges against them, and face 94 years in jail each if found guilty.
Police were alerted to the family after one of the daughters, a 17-year-old girl, escaped and told officers her siblings – aged between two and 29 – were being held captive.
The remaining 12 siblings were found by authorities “malnourished and very dirty” and shackled to their beds with chains and padlocks.