CORPUS CHRISTI, Texas — It's been more than a decade since Esteban Ruiz was sentenced to prison for the murder of a young woman in Corpus Christi, and investigators believe she wasn't his only victim.

It all started with evidence that came to light as he sat behind bars.

"I believe he was a serial killer," Prosecutor Joe Mike Pena said.

PART ONE: True Crime: Catching a Killer - A 3News Special Report

Convicted murderer Esteban Ruiz was sentenced to 40 years in prison for killing 29-year-old Devon Herrero; but as he sat behind bars, police soon learned their investigation into Ruiz was far from over.

"The possibility of multiple victims from the same offender started to grow," retired police Lt. Isaac Valencia said.

It was September of 2008, three months prior to the murder of Herrero, when a woman's body was found face up, fully clothed, and just yards away from the water's edge of the Oso. Her name was Kathleen Telge, a 42-year-old described as a loving mother and grandmother.

"Anyone who knew her knew she had a big heart," Telge's daughter said. "She did not deserve this."

An autopsy revealed Telge died from blunt force trauma to the head, but her case went unsolved until a new piece of information came from an unlikely source.

An inmate inside the same jail as Esteban Ruiz claimed that Ruiz had bragged about killing another woman.

"And we did have a girl that had been murdered, and the way the individual told us, information that came about matched up with the information that we received on the autopsy," Valencia said.

It was information that investigators said had not been released to the public.

It turned out the woman Ruiz bragged about killing was Telge, and DNA evidence backed up that allegation.

"I remember when we were checking the DNA and then a match was popping up on another victim, it was, 'Oh wow,'" Valencia said.

It was enough to try Ruiz in court, but the trial would be anything but typical. Prosecutors said there was a witness to the crime, but the problem was she was dead. It was Devon Herrero, who Ruiz admitted to killing months after he allegedly killed Telge.

After both the prosecution and defense finished their arguments, in a surprising twist, Ruiz made a highly unusual request.

Joe Mike Pena was one of the prosecutors on the case.

"The judge told the jury that the defendant wanted the judge to make the decision on the case on guilty or innocence," Pena said.

Ruiz put the decision in the hands of Judge Jack Hunter instead of the jury.

"It's sort of made-for-TV stuff isn't it?" Hunter said.

Ultimately he allowed it, finding Ruiz guilty not of murder, but of voluntary manslaughter.

Hunter said there was enough physical evidence to link Ruiz to the victim, but not enough to prove he knew she was dead when he dumped her.

"No matter what you do to a defendant, you know -- you could give them the death penalty, you could put them away for life -- there really is never justice for victims that lost their family members," Pena said.

Ruiz received the maximum sentence of 20 years for that crime.

"If he doesn't feel sorry for what he has done, he will pay for it in the end and God will make sure that happens," Telge's son said.

Meanwhile, authorities in Victoria County were investigating Ruiz for the death of another woman.

"So we knew we had two victims of crime from the same offender, and potentially a third," Valencia said.

That possible third victim was Velma Cierra, who was killed in 2007.

"There was that one case where we found more blood in his truck that didn't match up with any of the three victims," Pena said. "It makes you stop and wonder. He bragged about killing a third person in the Victoria area, but yet we never found the person to match up with the blood that was found in his truck."

Now 40 years old, Ruiz is currently in the Stiles Unit in Beaumont, Texas, where he will remain until the year 2068.

"He was just mad at women for some reason. What they are. We don't know," Pena said. "And he took it out on two women, and I'm convinced that he probably murdered a third woman out there, if not more. We may never know."

After all these years, an investigator with the Victoria County Sheriff's Office told 3News Esteban Ruiz is still considered a person of interest in Cierra's murder. The case remains open.

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