Washington (CNN) A man who was sexually abused by Dennis Hastert said Tuesday he was "surprised" that the former speaker of the House was released two months early from his 15-month prison sentence.

Hastert was released Tuesday from federal prison and is now under the supervision of a Chicago resident re-entry management field office after serving 13 months of a 15-month sentence . He pleaded guilty in October 2015 to a count of hiding money transactions.

"I was a little surprised," Scott Cross told CNN's Jake Tapper on "The Lead" in an exclusive interview. "I was a little, to be honest, a little disappointed in the sentence that was given out."

Cross stayed silent about his experience with Hastert for 37 years before coming forward during the investigation.

"You think about shame, guilt, embarrassment, humiliation -- the Hasterts of the world have so much trust and respect over you that you really have a hard time processing and understanding it," Cross said.

Since the investigation, Cross has worked with the Illinois attorney general to advocate for the removal of the statute of limitations for these types of crimes.

"It's more important that not just the state of Illinois change that -- there's only been a handful of states," Cross said.

"I hope by coming out and talking about this, other people have the courage to come out and speak out about this, whether its him or somebody else out there," Cross told Tapper.

The community Hastert and Cross came from was small, Cross said, with about 2,500 people.

"He was at the height of his popularity prior to going into politics," Cross said.

Cross testified in court about the fallout from Hastert's actions, saying he was "devastated."

"I tried to figure out why Coach Hastert had singled me out. I felt terribly alone. Today, I understand I did nothing to bring this on, but at age 17, I could not understand what happened or why," Cross said back in 2015.

"You made a difference in Illinois, kids in the future are going to see justice because of you and what you did, and hopefully some people out there will watch this show, find out what the laws are in their state, try to change it," Tapper told Cross. "So, thank you, Scott."

The investigation

What began as a look into questionable financial transactions eventually lead investigators to unearth a sexual abuse cover-up by Hastert.

Despite admitting to sexually abusing boys while working as a teacher and coach at an Illinois high school, he was never charged for any sexual crimes because the state's prior statute of limitations law barred prosecution.

The case came to light following a newspaper article in 2012 that involved allegations that Hastert was using taxpayer funds for personal use, FBI Special Agent Michael Anderson told CNN.

"He didn't tell us the truth when we met with him," Anderson said about the first interview with Hastert. "But he did welcome us, you know, into his home. And we got quite a bit of information that ultimately resulted in one of the charges against him, which was lying to the FBI."

Keen investigative work by the Internal Revenue Service, the FBI and the US Attorney's Office eventually discovered Hastert had agreed to pay $3.5 million in hush money to one individual in exchange for the former student's silence. Cross did not accept hush money from Hastert.

The IRS revealed that Hastert had been regularly withdrawing just under $10,000 in cash to give to a former student -- the dollar amount specific to avoid bank reporting requirements. This raised flags to investigators.

"Everything we do, we follow the money. In fact, the question we ask when we see suspicious activity is why. You know, why it's -- why would a rational person be taking out $9,000 over a three-year period of time more than 100 times," James Robnett, the IRS criminal investigation special agent in charge, said.

In addition to the prison sentence, Hastert also was eventually ordered to pay $250,000 to a victims fund.