(CNN) -- After years policing Illinois streets for criminals, Drew Peterson is now among them -- and will be for more than three decades, a judge ruled Thursday.
Will County Judge Edward Burmila sentenced Peterson to 38 years in prison in the murder of his third ex-wife, Kathleen Savio, said state's attorney spokesman Charles B. Pelkie.
The former Chicago-area police sergeant will get credit for the nearly four years that he has been in custody, according to Pelkie, a spokesman for Will County State's Attorney James Glasgow. He could have received as many as 60 years in prison; Illinois does not have a death penalty.
"The reason that I never looked Drew Peterson in the eye is because I never acknowledged his existence," said Glasgow, describing the convict as a "cold-blooded killer."
"But I looked him in the eye today," the prosecutor said. "He knows that we did our job."
Peterson's wife's fam reacts to verdict
Peterson was convicted of murder in September but had fought for a new trial, an effort that Burmila denied Thursday, just before the sentencing, Pelkie said.
Peterson's lawyers promised Thursday that they would press on with their appeal and expressed confidence they would prevail. They stood by their client, who made long and emotional remarks in court, claiming he never should have been found guilty of murder.
"Wouldn't you be angry if you were wrongly convicted?" said one of his attorneys, Steve Greenberg.
"In this case, (the prosecution) changed everything ... How would you feel if you were railroaded?"
Savio was found dead in her dry, clean bathtub on March 1, 2004. Prosecutors said Peterson killed her; the defense contended that she fell, hit her head and drowned.
The headline-grabbing case did not arise until after Peterson's fourth wife, Stacy, disappeared in October 2007. It was during the search for Stacy Peterson -- who still has not been found -- that investigators said they'd look again into Savio's death, which was initially ruled an accidental drowning.
Authorities altered their judgment and ruled Savio's death a homicide in February 2008, setting the stage for the first-degree murder trial last year of Peterson, a former police officer in Bolingbrook, Illinois.
A Will County jury convicted him of murder after nearly 14 hours of deliberation.
"Finally, somebody heard Kathleen's cry," the victim's mother, Marcia Savio, said after the verdict. "Twelve people did the right thing, oh, thank God."