Editor's note: This story contains graphic descriptions of alleged sexual abuse.
BELLEFONTE, PA (CNN) -- The alleged victim whose allegations triggered the criminal investigation into Jerry Sandusky is expected to take the stand Tuesday in the former Penn State assistant football coach's child rape trial, kicking off the second day of testimony in the high-profile case.
Michael Boni, a lawyer for the person identified in court documents as Victim 1, told CNN on Monday night his client is "ready to go."
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 Boni. He is contemplating scholarship offers from colleges, the lawyer adds.
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 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 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 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 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.
All about the allegations, how case unraveled
Besides the alleged oral sex, Victim 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 4 testified.
Jurors were shown excerpts of letters Victim 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 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.
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 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 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 4 in which the former coach wrote "I'm proud of you and really care."
The defense lawyer also questioned some alleged victims' behavior, like the one who went to a football game with Sandusky prior to his arrest.
Victim 4 brought his girlfriend and baby over to meet Sandusky "like he was bringing his family to meet his father," said the lawyer.
The alleged victim admitted Monday to visiting Sandusky about two years ago, so his girlfriend, who was suspicious about the past between the two, "could see that everything was normal."
"But that backfired because the whole time we were there, (Sandusky) only wanted to be with me and was sort of rubbing my shoulders. So (my girlfriend) knew," he testified.
Opinion: Jerry's got a jury of his peers -- HLN
In front of a screen showing childhood pictures of eight of the 10 alleged victims, prosecutor Joseph McGettigan detailed what he said happened to each in his opening statements.
"You'll hear about systematic behavior by a serial predator. These were experiences that took place not over days, not over weeks, not over months ... but over years," McGettigan said.
Feelings of humiliation, shame and fear led to "years of silence" on the part of accusers, the prosecutor said. He reminded jurors that Sandusky, not Second Mile or Penn State, was on trial. But, McGettigan said, Second Mile represented "the perfect environment for a serial predator."
In interviews after his arrest, Sandusky acknowledged showering and "horsing around" with boys, but denied being sexually attracted to them. McGettigan referred to those interviews during his opening statement, saying, "Deny what you can ... and make an excuse."
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.