DENVER — A Denver man serving a life sentence after being convicted of killing a 4-month old baby in 1998 is set to see his conviction erased Tuesday in light of new evidence that suggests the infant died from severe lung disease, not from being shaken.

Stephen Martinez, 58, was wrongly convicted of first-degree murder in the death of 4-month-old Heather Mares, his attorneys wrote in a petition for post-conviction relief filed Friday. Martinez was coerced into falsely confessing that he shook the baby and then received inadequate legal representation during his first trial, attorneys with the Korey Wise Innocence Project wrote.

In a response filed late Friday, prosecutors with Denver District Attorney John Walsh’s office agreed Martinez’s conviction should be vacated. Martinez is scheduled to appear Tuesday in Denver District Court, where both sides will ask Judge Andrew Luxen to erase Martinez’s murder conviction — and the life prison sentence it carries.

“Mr. Martinez is innocent and has served over 27 years for a crime he did not commit,” his attorneys wrote in the petition for post-conviction relief. One of his attorneys, Jeanne Segil, declined to comment Monday. She is the assistant director of the Korey Wise Innocence Project, an organization within the University of Colorado Boulder that provides free legal services to people who claim to be wrongfully convicted.

Matt Jablow, a spokesman for the Denver District Attorney’s Office, also declined to comment Monday.

New evidence shows that Heather died from a heart attack caused by severe respiratory illness, a condition that developed in the weeks before her death on Oct. 17, 1998, according to the petition. Martinez’s original attorneys failed to present any evidence of that ongoing respiratory illness at his original trial in 2000, so jurors were not able to consider other explanations for the baby’s death besides abuse by Martinez.

“The People agree there is a reasonable probability that, but for that failure, the outcome of the trial would have been different,” the prosecution’s response reads. “…This court should vacate Mr. Martinez’s conviction.”

Andre Mares, a relative of Heather’s, said Monday that their family believes the conviction should stand and anything else would be an injustice.

“It’s almost like justice forgot about Heather,” he said. “I know that, on the one hand, they are always trying to make sure the right man is convicted, but considering the evidence and what Stephen Martinez said he did, to come back and say, ‘It’s pneumonia’ — it is mind-boggling what justice will swallow.”

Martinez, who was dating Heather’s mother, was alone with the baby for 15 minutes at their home in the 400 block of South Pecos Street on Oct. 17, 1998, when he called 911 to report that the baby was choking. Martinez told first responders that he gave Heather a bottle because she was crying, then put her down and went into another room. He returned to the infant a few minutes later when he heard her choking.

“She was gasping,” Martinez wrote in a statement during the investigation. “…I put my finger in her mouth and throat to see if there was something stuck in there. She then started spitting up blood and gasping harder.”

First responders were unable to save Heather’s life. Further investigation showed that the baby had suffered a skull fracture, ruptured blood vessels in her eyes, brain bleeding and swelling. At the time, medical and child abuse experts saw those injuries as tell-tale signs of child abuse, but now, experts recognize that many other situations can also cause those injuries, his attorneys wrote.

During a middle-of-the-night interview with a Denver police detective, Martinez confessed to shaking Heather and slamming her into a crib — a confession that he later recanted and which his attorneys say was false. Martinez also told police he tripped while holding the baby a couple weeks before her death, which he thought might have caused her skull fracture. Heather’s mother told investigators that Martinez sometimes became angry when Heather cried.

Martinez’s attorneys note he confessed to shaking the baby only after the detective suggested it would have been reasonable for him to shake the baby during a moment of frustration, and that by admitting to doing that, he might receive a more lenient sentence. His confession does not match the physical evidence in the case, they wrote.

During the trial in 2000, prosecutors described Heather as healthy and behaving normally until she suddenly died in the brief window she was alone with Martinez. But in reality, the girl was sick for weeks before she died, according to the petition.

Heather spent time in neonatal intensive care after her birth for trouble breathing, had a respiratory infection when she was 2 months old, went to urgent care when she was 3 months old for a fever and spitting up blood-tinged milk, was sick the night before she died, and choked on the morning of her death when her mother gave her a bottle, Martinez’s attorneys wrote.

Doctors who recently reviewed Heather’s case found that her lungs were severely damaged to the point that “she had almost no air,” according to the petition. Her lung infection could have caused the symptoms that were previously attributed to abuse, the experts found, and the fall that Martinez described a couple weeks before her death could have caused the skull fracture.

Current science does not support the notion that Heather’s injuries were caused by shaking, according to the petition.

“There is now no credible evidence that Mr. Martinez caused (Heather’s) death,” the petition reads.

Martinez has maintained his innocence for decades. In earlier appeals, his conviction was reversed by the Colorado Court of Appeals in 2001 over concerns about whether some expert testimony given during his trial was legally permissible. The Colorado Supreme Court reversed the Court of Appeals’ ruling and upheld Martinez’s conviction in 2003.

_________

©2026 MediaNews Group, Inc. Visit at denverpost.com. Distributed by Tribune Content Agency, LLC.