Spoiler alert: This article contains details from episode three of WNYC's "Dead End" podcast.

Detectives in Somerset County in New Jersey made several crucial mistakes in their investigation into the deaths of John and Joyce Sheridan, a prominent couple with close ties to four New Jersey governors. Based on interviews and an examination of physical evidence at the crime and autopsy documents, an investigative podcast from WNYC Studios found those mistakes led the detectives to erroneously declare the crime a murder-suicide.

The 2014 grisly murder has gone unsolved by the Somerset County Prosecutor’s Office. Investigators initially believed John Sheridan killed his wife and then himself, but the state changed John Sheridan’s death certificate in 2015 to remove the suicide determination and left his manner of death listed as “undetermined” since then.

The couple was found dead in their home in Skillman, N.J., just outside Princeton. John Sheridan worked for two gubernatorial administrations and served as the commissioner of transportation. He and Joyce Sheridan were stabbed to death in their bedroom and the house was set on fire.

“When fires are started, it's usually started by an individual who wants to destroy evidence, fingerprints, DNA, whatever,” said Dr. Michael Baden, an independent medical examiner who was hired to perform a second autopsy by the Sheridan family.

Baden determined that the knife that killed John Sheridan was not found at the scene, contradicting the detectives murder-suicide theory. .

“Usually when people commit suicide using a sharp weapon, the weapon is found at the scene,” he said. “So those are features that struck me as indicating that this was not at all a typical suicide or suicide homicide.”

Here is what detectives decided after they examined the crime scene on the morning of the Sheridans’ deaths:

The blocked bedroom door: When firefighters arrived at the Sheridan house just before dawn on September 28th, 2014, they struggled to get into the bedroom. Once they got inside, they saw that a large armoire was blocking the door from the inside. They concluded there could not have been an intruder.

Valuables are everywhere: There was $950 in cash on the bedside table, an iPad, prescription opioids (Joyce Sheridan had chronic pain from a back injury), and expensive jewelry. This led detectives to decide that this wasn’t a robbery or a drug deal gone bad.

Blood in the stairwell: Forensic technician Barry Jansen was told not to bother photographing the stairwell, which had blood on the lower parts of the walls and stairs. He was told that blood was spilled when firefighters carried the bodies down the stairs.

Different wounds: The knife attack against Joyce is more vicious and she has defensive wounds on her hands. Sheridan’s knife wounds are smaller, there are fewer of them, and detectives believed he didn’t have defensive wounds. This leads detectives to believe John killed Joyce and then himself.

No Forced Entry: There were no signs on the doors or windows that the house had been broken into.

The latest episode of “Dead End: A New Jersey Murder Mystery” finds evidence that contradicts the initial theory that the Sheridans’ death was a murder-suicide:

The blood spatter: Detectives didn’t document or take samples of a blood spatter high on the wall in the stairwell. “When you see a blood splatter, that shows direction,” said Eddie Rocks, a retired homicide detective from the Philadelphia Police Department. “Usually you see the splatters where there's a confrontation, where there's movement.” This contradicts the detectives’ theory that John Sheridan stabbed himself with the kitchen knife in the bedroom.

The fire poker: A four-foot-long wrought iron poker is found in the bedroom by an insurance investigator a few weeks after the couple’s death. It hadn’t been taken into evidence. John Sheridan had thin bruise marks across his chest, four broken ribs and a chipped tooth, the autopsy found.

The missing knife: Detectives found two kitchen knives in the bedroom, a serrated bread knife and a carving knife. The autopsy found that Joyce was killed by the carving knife. Detectives believed the smaller knife wounds on the body of John Sheridan were caused by the same knife, but he had struggled to stick himself so they didn’t penetrate deeply. A second autopsy by an independent medical examiner found that the knife that killed John had a narrow blade, like a stiletto. No such knife was found in the bedroom.

The back stairs: The Sheridans’ bedroom had a back door that led to a second set of stairs. But detectives missed this and thought no one had left the room once the violence had begun. The evidence shows the back door was open during the attack because there was blood across the threshold of the door. But smoke stains left an outline of suits that were hanging on the inside of the door, which shows it was closed during the fire.

Defensive Wounds: Joyce Sheridan had defensive wounds on her hands, showing she tried to protect herself during the knife attack. Detectives didn’t see knife wounds on John Sheridan’s hands. But one of his hands was badly burned in the fire, so it wouldn’t have been possible to determine if John Sheridan had defensive wounds.

DNA Evidence: Analysis of a tiny fragment of DNA on the handle of the knife that killed Joyce is male DNA that could not have come from any member of the Sheridan family.

Unlocked Door: The Sheridans were known to have kept their door unlocked, which means an intruder could enter the house without leaving any sign of a forced entry.

An illustration of a home burning at the end of a cul-de-sac. The words "Dead End: A New Jersey Political Murder Mystery" is written along the top.

"Dead End" is a story of crime and corruption at the highest levels of society in the Garden State.

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"Dead End" is a story of crime and corruption at the highest levels of society in the Garden State.
Liam Eisenberg for WNYC Studios

New episodes of “Dead End: A New Jersey Political Murder Mystery” from WNYC Studios are available now, anywhere podcasts are available.