A Brooklyn judge threw the book at a serial rapist who sexually assaulted four women in one week — including a 15-year-old girl — sentencing him to 100 years in prison.

Dexter Bell, 26, who committed a series of rapes in the alleys and stairwells of Crown Heights in 2013, had previously been convicted in the rape of a 17-year-old girl in 2008.

Bell also sexually assaulted a correction officer earlier this year while being moved from Rikers Island.

He was found guilty on six counts of predatory sexual assault by a jury on Nov. 9, and sentenced Monday by Judge Vincent Del Giudice in Brooklyn Supreme Court.

“What Dexter Bell did to me changed my life forever. Even after two years, I don’t feel as safe,” a 25-year-old victim, attacked in April 2013, wrote in a statement submitted to the court.

“Bell deserves to go to jail for a very long time. Not just because of what he did to me but so he never does this to anyone else ever again.”

From April 4 to April 11, 2013, Bell approached four victims and started conversations. He then pulled them by their arms or hair into a solitary area and raped them.

When he was arrested, he was carrying a handwritten note detailing the dates and times of two of the rapes, Detective Jonathan Cruz testified during a pretrial hearing.

“This serial rapist, who committed four rapes within one week, including one of a 15-year-old girl, is a sadistic and violent sexual predator who is simply not fit to walk the streets ever again. That’s why he must spend the rest of his life behind bars,” Brooklyn DA Ken Thompson said.

Bell was finally nabbed after an anonymous tipster called the police with the attacker’s name and address after seeing news stories about the assaults.

The youngest victim also submitted a statement, which was read to the court.

“I’m glad that you got caught because I don’t want this to happen to any other females,” the statement said.

“I would never want any other females to have to go through what I went through. I was only 15 years old. Why would you do that to me?” she wrote.

“How would you feel if someone did this to you? How would you want someone to treat your mother, sister, or your daughter?”