SPRING, Texas -- A former substitute teacher in the Houston area is behind bars after allegedly performing a sex act on a student while he was asleep.According to charging documents, 35-year-old Manuel Gamboa invited the 17-year-old male student to his home in Harris County after giving the student beer on June 3.Gamboa was a substitute teacher at Dekaney High School at the time of the alleged crime."Complainant stated that he consumed several beers and became dizzy due to him not normally drinking," charging documents stated.The victim also told investigators that Gamboa was "like a mentor to him and helps him with his homework due to him not knowing any English."Inside the home, the victim said that he didn't feel well and went to sleep on the living room sofa bed.When the victim woke up, he says, Gamboa was next to him.Charging documents state that the victim told police that he felt discomfort and minor pain while urinating.When the victim went to use Gamboa's cell phone, he noticed sexually explicit videos and images on the phone.The victim stated that there were images of Gamboa performing oral sex on him while he was asleep and without his permission, according to documents.Charging documents also stated that a sexual assault exam performed at a hospital confirmed evidence of DNA on the victim that wasn't his.Gamboa was arrested Wednesday and charged with improper relationship with a student and sexual assault. He is being held on $80,000 bond.