In 1987: A Double Murder in Dallas Built on Junk Science
Today in True Crime
by CaseBond · Source-backed daily true-crime history
June 20, 2026
In 1987: A Double Murder in Dallas Built on Junk Science
On the night of June 20, 1987, John Sweek and his wife Sally were found dead inside their Dallas, Texas apartment. John was twenty-seven years old; Sally was twenty-one. The crime that ended their lives would also begin the wrongful destruction of another man's — a slow-motion miscarriage of justice that would take more than twenty-five years to reverse.
Dallas investigators processing the crime scene recovered numerous pieces of physical evidence. Among the findings was what appeared to be a human bite mark on one of the victims. This detail would prove decisive in the prosecution that followed — not because it pointed to the true killer, but because it pointed to a forensic technique that courts had long treated as reliable and that, in the decades to come, would be thoroughly discredited.
Several days after the murders, an anonymous caller contacted police with information implicating a man named Steven Mark Chaney. The caller claimed that he and Chaney had been regular visitors to the Sweek apartment, buying cocaine there multiple times a week. A second source told investigators that Chaney owed John Sweek money — a potential motive. Investigators had a name, a motive, and a forensic clue. They had what looked like a case.
Chaney himself told investigators he had eight witnesses who could account for his whereabouts on the night of June 20. He also said he had not been inside the Sweek apartment in the weeks before the murders — directly contradicting the picture the anonymous caller had painted. These were significant facts, but they were not enough to stop the prosecution from moving forward.
In 1989, Chaney stood trial for the murders. The prosecution's centerpiece was testimony from two forensic odontologists who told the jury that bite marks found on one of the victims matched Chaney's teeth. It was the kind of expert testimony that juries take seriously — specific, technical, delivered with professional confidence. The jury convicted Chaney on both murders and sentenced him to life in prison.
He served more than twenty-five years. Meanwhile, the scientific consensus on bite mark analysis was eroding. Researchers and review bodies, including the National Academy of Sciences, were reaching a stark conclusion: the foundational assumptions of bite mark matching — that teeth are sufficiently unique and that marks on human skin can be reliably linked to a specific individual — had never been scientifically validated. The technique, presented in 1989 as settled forensic science, was increasingly being characterized as junk science. Under Texas law, a conviction obtained through discredited science can be challenged on that basis alone.
The Dallas County district attorney's Conviction Integrity Unit took up the case, reviewed the odontology testimony against the evolving scientific standards, and brought the matter before the Texas Court of Criminal Appeals. In December 2018, the court formally declared Steven Mark Chaney an innocent man. He walked free after a quarter century of wrongful imprisonment — officially cleared, the conviction vacated.
The murders of John and Sally Sweek on June 20, 1987 remain officially unsolved. The real killer has never been identified. What the Chaney case leaves behind is a clear inventory of how a wrongful conviction assembles itself: an anonymous tip that could not be cross-examined, a forensic technique that turned out to be scientifically unsound, and a prosecution built on the combination of both. The criminal justice system ultimately corrected its error. It took more than twenty-five years.
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Sources used/checked for this issue
- Steven Mark Chaney, Innocence Project — "Steven Mark Chaney," Innocence Project. https://innocenceproject.org/cases/steven-mark-chaney
- Texas court throws out 1987 murder conviction; declares North Texas man innocent, Texas Tribune — "Texas court throws out 1987 murder conviction; declares North Texas man innocent," Texas Tribune, December 19, 2018. https://www.texastribune.org/2018/12/19/steven-mark-chaney-murder-conviction-overturned
- Man declared innocent in 1987 murder under Texas junk science law, UPI — "Man declared innocent in 1987 murder under Texas junk science law," UPI, December 19, 2018. https://www.upi.com/Top_News/US/2018/12/19/Man-declared-innocent-in-1987-murder-under-Texas-junk-science-law/4791545260268
- Chaney v. State, No. 05-87-01371-CR (Tex. App. 1989), Justia — Chaney v. State, No. 05-87-01371-CR, Texas Fifth Court of Appeals (1989). https://law.justia.com/cases/texas/fifth-court-of-appeals/1989/05-87-01371-cr-6.html
- Chaney, Steven Mark — Forejustice Database, Forejustice — "Chaney, Steven Mark," Forejustice Database. http://forejustice.org/db/Chaney--Steven-Mark-.html
Today in True Crime by CaseBond — 2026-06-20
