Naman Shrestha
The episode titled ‘Lying Consequences’ of Investigation Discovery’s ‘911: Did the Killer Call?’ chronicles the untimely and tragic death of a 4-month-old girl named Heather Mares in Denver, Colorado, in October 1998. As the detectives investigated the mystery behind her demise, they connected it to a suspect who maintained his innocence even after his conviction. Years later, as new evidence emerged, the investigation took an unexpected turn.
Heather Mares Died in the Absence of Her Mother
Born in June 1998, Heather Lynn Mares was the beloved daughter of Kimberly Estrada, who was raising her in Denver, Colorado. Four months after her birth, a tragedy took place at the house located off Pecos Street. On October 17, 1998, the police received a 911 call from the residence where Heather was being raised by Kimberly. After arriving at the site, they found Heather in a critical condition and rushed her to the Denver Health Medical Center, where she was later pronounced dead. The doctors at the hospital concluded that 4-month-old Heather had sustained a fracture in the skull, which caused bleeding inside her brain. They also told the investigators that her head injury was most likely a result of the girl’s head striking against a hard surface and not by choking. Given the suspicious cause of death, a homicide investigation was launched.
Heather Mares’ Suspected Killer Made a Chilling Confession
During the investigation, the police learned that Heather Mares lived with her mother, Kimberly Estrada, and her boyfriend, Stephen Martinez, who called the police and reported that the baby was choking. They learned that Kimberly left her daughter with Stephen and headed to the bank for a quick errand. The mother told the detectives that Stephen was allegedly jealous of her children, claiming that he used to get angry when Heather cried. During his interrogation on October 18, 1998, Stephen told the police that he heard choking noises while he was home alone with the child.
He said, “I was sitting there eating, and I heard Heather, she started, like, gasping, choking, even. So I put my plate aside and I went in there and just… She was in distress, that’s for sure. I did a finger sweep because I thought maybe she grabbed a little toy or something. I picked her up, and I’ll just pat her on the back. And then she threw up on me, but it looked like blood and baby formula.” Stephen claimed that when she wasn’t getting any better, he called 911 and followed the operator’s instructions. While inspecting the house, the detectives also found Heather’s blood-stained sheets in the washing machine. When confronted with it, Stephen claimed that the blood was due to the vomit, and he had removed the sheets and his clothing to clean up the mess.
The suspect also told the investigators that he tripped on a telephone cord while holding Heather about two weeks prior to her demise. At the time, he thought he had protected her head during the fall, but during the interrogation, he thought her head injuries could have been caused by that fall. Later during the interview, Stephen confessed to shaking Heather hard and hitting her head on her crib. After his confession, he was placed under arrest and charged with the murder of Heather Mares.
Stephen Martinez Has Been Released From Prison After Serving Decades Behind Bars
In early 2000, Stephen Martinez stood trial for the homicide of 4-month-old Heather Mares. During the trial, the prosecution brought two expert witnesses who explained how Heather had died from blunt force trauma to the head caused by shaken-impact syndrome. After the jury found Stephen guilty of first-degree murder, he was sentenced to life in prison without the possibility of parole. Although his sentence was overturned by the Colorado Court of Appeals in 2001, the Supreme Court reinstated his sentence in 2003. His appeals for postconviction relief were rejected by the court in 2006 and 2012. Years later, in April 2026, the Korey Wise Innocence Project (KWIP) filed a motion on Stephen’s behalf, supported by detailed expert reports that conclude Heather died from severe lung disease instead of blunt force trauma.
After five other medical experts reached the same conclusion, Stephen’s hearing took place on April 21, 2026. At the court hearing, Heather’s mother, Kimberly Estrada, requested the judge to uphold the conviction. She stated, “Your Honor, please, I beg you, don’t let him out; we don’t deserve that. I don’t deserve that. From our family to yours — if you have one — please don’t let this animal out on the street. He doesn’t deserve it, and neither do we…I need to know my other children will be safe in this world.” In the end, Stephen’s case was dismissed, and he was released from prison. Later, Kimberly told Denver7 that she still believed Stephen was guilty of killing her child, stating, “I still have questions that I want answered that will probably never get answered,” said Estrada. “We wanted that opportunity to look at him face-to-face and ask him, ‘Why?'”
Meanwhile, Stephen stated, “I’m finally going to be made righteous, because they pinned this on me. They made me out to be a monster.” The following month, in May 2026, he shared how freedom felt after decades of incarceration in a conversation with People. “This feels wonderful, amazing, just an incredible feeling to be able to leave all that steel, concrete, razor-wire behind and be made righteous and come back into society with a new beginning, a new start,” he stated. In 2023, Steven reportedly reconnected with his now-wife, with whom he leads a fresh life after his release. Talking about adjusting to technology, he said, “It’s been challenging, and fun, and sometimes frustrating, but it’s been an overall joy being able to get out into this whole new world that changed and left me behind, and get to use new technology.”
Having spent a lot of time reading and studying while incarcerated, Stephen expressed his desire to “take some online courses or maybe go to community college and become a counselor, maybe a mental health person.” He also hopes to become an advocate for innocent people behind bars. As of today, he prioritizes his wife and family, working hard to “better myself, to become a better person, a better father, a better husband, a better uncle, a better cousin,” while keeping himself away from the limelight.
Read More: Doris Cumming Murder: Where is Robert Tincher III Now?
You must be logged in to post a comment.