Update: On Wednesday afternoon, right on schedule, former House speaker Dennis Hastert (R-Ill.) surrendered himself to prison, the latest development in an incredible fall from grace for a man who was once one of the nation's highest-ranking elected officials. Our post catching you up on all the case's details is below.

Hastert will serve  15 months in a federal prison hospital in Minnesota for illegally paying money to keep an alleged sex abuse victim quiet. (The Chicago Tribune reports the sentence is expected to be about 12½ months with credits for good behavior.)

Hastert is among the highest-ranking American politicians ever to serve jail time. He's the first former U.S. House speaker to be convicted and sentenced in a criminal case, and the first former speaker since the 19th century to be incarcerated.

It's a stunning fall from grace for the longest-serving Republican House speaker, who had apparently been carrying around a dark secret from his past as he rose to and then served in Congress's top job from 1999 to 2007.

Here's a quick recap of the case and Hastert's sentencing.

What, exactly, he did wrong

Hastert pleaded guilty in October to charges that he violated federal banking laws and lied to the FBI to keep secret the fact that he molested a high school wrestler he coached. (Scroll down for more on that.)

But the reason he's going to prison is less about the sexual abuse allegations and more about the banking laws he broke while trying to to keep an alleged victim quiet — and lying to the FBI about it as they started investigating.

How it unfolded

Hastert first drew attention from the FBI and IRS three years ago for withdrawing large amounts of cash from various banks. Investigators first thought Hastert was being extorted; The Washington Post's Matt Zapotosky reported that Hastert claimed as much in an interview with investigators. Hastert said a man was making false claims that Hastert had molested him.

Investigators looked into it but soon suspected it was Hastert who might be lying.

Zapotosky reported: "After listening to Hastert talk to the man he alleged was blackmailing him on a recorded call, though, FBI agents were skeptical. And when they interviewed the man, they concluded that he was making believable claims. Other victims emerged with similar stories."

The law Hastert actually broke

Hastert admitted in October that he withdrew money in increments just small enough to avoid having to report them.

Federal law mandates cash transactions exceeding $10,000 be reported using a Currency Transaction Report, The Fix's Philip Bump reported in May of 2015: "The reason for this is pretty obvious: It is meant to allow criminal activity to be traced. It is also illegal to break up large transactions into smaller ones to avoid the reporting requirement. That's known as 'structuring.'"

Investigators later pieced together that Hastert was trying to pull out money to buy silence from a man who accused him of sexual assault. According to court documents, the man said Hastert agreed to pay him $3.5 million. To do so, Hastert engaged in structuring.

It is not necessarily illegal to pay someone hush money.

The sex crimes angle

Federal investigators did not charge Hastert with sexual misconduct, though they said they wanted to. There are five alleged victims from the former congressman's days as a high school wrestling coach in the 1970s. Several of them spoke powerfully at Hastert's sentencing hearing in April. (Scroll down for more on that.)

U.S. attorneys told reporters at Hastert's sentencing that they originally wanted to pursue the sexual misconduct charges but that the statute of limitations had run out. And they agreed to a plea deal with Hastert on the banking laws because one of Hastert's alleged victims didn't want to have to take the stand during a trial.

The closest Hastert ever got to admitting the sexual misconduct was telling a courtroom at his April sentencing he was "deeply ashamed" to be in court and that he "mistreated some of my athletes that I coached."

The sentencing

It was an emotional day for many involved on the case. Hastert, now 74 and in deteriorating health, was rolled into the Chicago courtroom in a wheelchair.

The frail former speaker stared straight ahead as an accuser and another accuser's sister directly confronted the once-powerful politician with decades of welled-up pain and anger:

Hastert's moment of judgment came, and U.S. District Judge Thomas Durkin didn't need much time to think about it. He said Hastert was a "serial child molester" and ordered him to undergo a sex offender treatment program.

Then the judge switched to the legal matter at hand -- violating federal banking laws -- and sentenced Hastert to 15 months in prison, a punishment above what federal prosecutors had suggested.