Bellefonte, Pennsylvania (CNN) -- The man whose accusations of sexual abuse helped trigger a criminal investigation, upending the storied Penn State football program, said Tuesday that he stayed at Jerry Sandusky's house more than 100 times as a boy, where the former assistant football coach repeatedly sexually abused him.
Now 18, the man identified as "Victim No.1," said he grew up without a father, living with his mom and siblings, and had met Sandusky at Second Mile, a foundation the former coach founded for needy children.
"At first he would kiss me on the forehead goodnight," Victim No.1 testified Tuesday. "Then it was kissing me on the cheek, then rubbing my back and cracking my back."
Sandusky's roaming hands would later move to "rub underneath my shorts," he said. The alleged abuse further escalated when Sandusky "put his mouth on my privates."
"I spaced," he said. "I didn't know what to do."
Later, the former coach allegedly told him that "it's your turn," the man added. "He made me put my mouth on his privates."
The man's emotion-filled descriptions kicked off the second day of testimony in the high-profile case.
The grand jury report cited evidence that Sandusky, who met the boy when he was 11 or 12 years old, "indecently fondled Victim 1 on a number of occasions, performed oral sex on Victim 1 on a number of occasions and had Victim 1 perform oral sex on him on at least one occasion."
The teenager, who transferred schools amid the fallout from the Sandusky investigation, graduated from his new high school this past weekend, according to his attorney Michael Boni.
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He is one of 10 boys who, prosecutors say, were sexually abused by the Nittany Lions' longtime defensive coordinator over a span of 15 years. Sandusky's trial on 52 charges is expected to continue for about three weeks.
The first person to take the stand Monday after opening statements was a now 28-year-old man identified as Victim No. 4. He said that Sandusky routinely had the then-teenage boy perform oral sex on him while the two showered together on the school's campus and elsewhere
"It would have to be 40 times, at least," he said, adding that the abuse started when he was 14.
The man on the stand Monday, as well as Victim No.1, met Sandusky through Second Mile, the nonprofit group the ex-coach founded.
He described growing up without parental oversight before Sandusky took to him -- playings sports with him, paying for uniforms, a snowboard and other items, taking him to Penn State games and doing other special things. Victim No. 4 said Sandusky also drove him to buy marijuana once when he was 15 or 16 and had bought him cartons of cigarettes.
Despite what he described as systemic sexual abuse by Sandusky, the witness said he was "scared" and reluctant to talk about it and "lose the good things I had." But he said he decided to tell his story after hearing that "this happened over and over and over again."
While Sandusky said he wanted him to succeed and was nice to him in public, Victim No. 4 said their relationship was different in private.
"He treated me like a son in front of other people. Outside of that, he's treating me like his girlfriend," he said, noting Sandusky's habit of putting his hand on the then-teen's thighs when they drove in a car together.
Besides the alleged oral sex, Victim No. 4 detailed other instances of alleged abuse, including Sandusky trying to penetrate him in the shower, caressing him and "kissing ... my thighs."
This allegedly took place in athletic buildings on Penn State's campus, as well as the Toftrees Golf Resort and hotels, including on trips to Florida and Texas to watch the Nittany Lions play at the Outback and Alamo bowls, respectively, Victim No. 4 testified.
Jurors were shown excerpts of letters Victim No. 4 said Sandusky wrote to him. In one, it states, "I know that I have made my share of mistakes. ... My wish is that you care and have love in your heart. Love never ends."
Defense attorneys had filed a motion earlier Monday seeking to keep out testimony involving prosecutors' allegations Sandusky exhibited "grooming behavior," including the letters to Victim No. 4.
The lawyers said they intend to offer expert testimony from a psychologist who "will explain that the words, tones, requests and statements made in the letters are consistent with a person who suffers from a Histrionic Personality Disorder," the documents said.
According to the National Institutes of Health, those with histrionic personality disorder "act in a very emotional and dramatic way that draws attention to themselves."
"The goal of a person suffering from this disorder in writing those letters would not necessarily be to groom or sexually consummate a relationship in a criminal manner, but rather to satisfy the needs of a psyche belabored by the needs of such a disorder," the defense lawyers write in their motion.
Prosecutors also say Gary Schultz, a former Penn State vice president who oversaw campus police, held a file that detailed alleged incidents pertinent to the investigation of Sandusky.
Schultz and Tim Curley, Penn State's former athletic director, have pleaded not guilty to charges of perjury and failing to report an alleged sexual assault of a child.
The file, which prosecutors say was initially withheld during the investigation, shows inconsistencies with what Schultz and Curley told a grand jury, according to court documents filed by prosecutors and obtained by CNN Tuesday.
"The Commonwealth is entirely justified in using those documents as evidence to support the charge of perjury against Schultz," the court documents say.
Prosecutors say e-mails from Schultz, Curley and others further contradict that testimony.
The firm representing Louis Freeh, an ex FBI Director investigating Penn State's handling of the scandal, said Tuesday that his office "discovered these e-mails in the course of its work."
"These e-mails were then provided to the State Attorney General, consistent with the investigation's prior commitment to share certain information," the firm said. "These materials will be fully discussed in the report to the Task Force, and beyond that Judge Freeh and the investigation team has no further comment."
In opening statements, defense lawyer Joe Amendola suggested his client would take the stand and say he routinely "got showers with kids" after working out.
Sandusky has always maintained his innocence, Amendola said, claiming his client's alleged victims had changed their stories and were questioned until authorities received the answers they wanted.
"A lot of people lied," Amendola said. Some of the alleged victims have civil attorneys, he noted, calling that unusual. Others, he said, have a financial interest in the case.
"One of the keys to this case, one of the keys to your perception ... is to wait until all the evidence is in," Amendola told jurors. "Some of it will be graphic ... it's going to be awful. But that doesn't make it true."
Tom Kline, an attorney for Victim No. 5, told reporters later that his client had no financial interest and "never sought this out," but considers it "an obligation of citizenship" to testify.
And Victim No. 4 said he's never talked with his lawyer, whom he said he hasn't paid "a dime," about being part of any civil lawsuit against Sandusky.
Amendola told jurors former Second Mile children will testify that Sandusky affected their lives in a positive way, and he later showed a letter to Victim No. 4 in which the former coach wrote "I'm proud of you and really care."
The defense lawyer also questioned some alleged victims' behavior, including one who went to a football game with Sandusky prior to his arrest.
A jury of five men and seven women, along with four alternates, was selected last week. Half of the 16 jurors and alternates have ties to Penn State, including one retired professor and one current professor, three graduates, two employees and one current student, showing the prominence of the university in the local community.
The case has raised questions about Penn State's response to allegations, with some claiming the school put its reputation ahead of protecting potential child victims.