UPDATED 03/06/12 – 8:48 p.m.

CHICAGO (CBS) — William Heirens, the so-called “Lipstick Killer” jailed for more than 65 years after confessing to the murders of three women and a 6-year-old girl around the end of World War II, has died in prison.

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Heirens, 83, was found unresponsive in his cell at Dixon Correctional Center. He was later pronounced dead at the University of Illinois at Chicago Medical Center.

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He had been suffering from renal failure and hypertension, reports WBBM Newsradio’s Bernie Tafoya.

Heirens was the longest-serving inmate ever in Illinois. He was convicted first of the 1945 slayings of Frances Brown, 32, and Josephine Ross, 43, in their apartments in Uptown and East Lakeview, respectively. He was also convicted of the dismemberment of 6-year-old Suzanne Degnan, of the Edgewater neighborhood, the following year.

CBS 2’s Dana Kozlov spoke to Degnan’s sister about the murders and Heiren’s death.

“He was sick,” Betty Finn said. “After he murdered Suzanne and dismembered her, he just walked over to the ‘L’ and took the ‘L’ down and went to class at the University of Chicago. And that’s not a normal person.”

Degnan’s remains were found scattered near the family’s Rogers Park home shortly after her 1946 disappearance. Heirens, 17 at the time, was soon arrested and confessed to a slew of robberies and eventually to killing Degnan and two other women. But it was a confession he took back and claimed evidence against him was tainted.

“Back in ’46, I buckled under. When the pressure’s on, you go the way they want you to go,” Heirens said several years ago about his confession.

But Finn said she never bought that, and she spent decades fighting to keep Heirens from getting paroled.

“After he was caught, his horrible crimes stopped,” Finn said.

Heirens was known as the “Lipstick Killer” because of a message scrawled in lipstick in Brown’s apartment, at 3941 N. Pine Grove Ave. in the East Lakeview neighborhood: “For heavens sake catch me before I kill more. I cannot control myself.”

At the time, Heirens was 17 and attending college at the University of Chicago. He was sentenced to three life prison terms.

But there have been nagging doubts about Heirens’ convictions for decades.

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In 1995, attorney Jed Stone told CBS 2 that a reexamination of the case showed that fingerprint evidence used against Heirens was “fraudulent” and may have been planted at one of the murder scenes by police. Experts also said handwriting samples used against Heirens were not actually his.

Heirens himself maintained all along that he confessed only because authorities said he would get the death penalty if he did not.

Heirens told CBS 2’s Walter Jacobson in 1988 that he decided to confess “when they told me I wasn’t going to get a fair trial – they said, ‘There is no possibility you are going to get a fair trial.’ Back in ’46 at 17, I wanted to live.”

Finn said she never had a moment’s doubt that Heirens strangled her younger sister and threw her dismembered body parts into sewers around her home on Kenmore Avenue.

“We outlived him,” said Finn, who was just 10 years old when her sister was kidnapped from her bend and brutally murdered.

But others, like Heirens’ attorney, do have doubts. Stone said he feels a sense of guilt that he could never clear Heirens’ name.

“He was bright and personable; so much not the boogeyman, and so much not a murderer,” Stone said. “So, when I heard that he had passed, I was sad. I was also moved by the fact that I had failed him, because I tried to get him out. I tried to give him some life of freedom, and I couldn’t do it.”

Finn said that is something for which she is thankful.

“I hope he did make amends with God, and died in peace, I hope,” she said.

After his arrest, Heirens was given sodium pentothal and questioned for six days without an attorney. Those were some issues his attorneys tried to use to clear his name.

Heirens was 83 years old and spent almost 66 years behind bars.

While he was in prison, Finn went before the Illinois Prisoner Review Board year after year to oppose parole for him.

“(It’s) very painful to have to do that. But we just felt that if we didn’t do it – my brother and I – and he got out and some child was hurt, we just couldn’t live with that,” she said.

Heirens was most recently up for parole in 2007, but it was denied.

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Finn says she can breathe much easier now that she knows she’ll never have to again publicly relive the horror of what Heirens did.