Three months after the investigation into the violent deaths of John and Joyce Sheridan began, key details of the case remain unexplained, and authorities have continued to interview people who knew the couple.

The Somerset County Prosecutor's Office, the lead agency handling the case, has not said who or what led to the deaths 91 days ago of the Sheridans - John, Cooper Health System's chief executive, and Joyce, a retired teacher. Nor has it said who set the fire in the couple's master bedroom, where the pair were found with stab wounds.

In its last public statement about the case, on Nov. 19, the Prosecutor's Office said: "Complexities involved with this case warrant a thorough and exhaustive review." That statement followed news that state officials had joined the investigation.

"It's very frustrating," said Peter Mitchko, 72, Joyce Sheridan's brother. "How can you not offer up any information?"

Though it is unclear whether authorities have discovered new evidence in recent weeks, sources familiar with the case said investigators had been struggling with wounds on John Sheridan caused by a weapon or weapons they initially could not find among the rubble.

The Sheridans were found unresponsive Sept. 28 during the early-morning fire in the second-floor bedroom in their house in the Skillman section of Montgomery Township.

Investigators, two sources with knowledge of the case said, initially theorized John Sheridan killed his wife before setting the bedroom on fire and taking his own life. Some experts said that seemed unlikely based on the limited public information about the case, especially, one source said, because John Sheridan was found under an armoire.

"I've never seen anything like this," said Gil Scutti, a criminal defense lawyer and former assistant U.S. attorney not involved in the case. He, like other experts, said it was hard to conclude murder-suicide based on the details that have now gone public.

"I don't see why someone would go to such lengths to cover up a murder-suicide, assuming it was physically possible for him to do it," Scutti said.

Philadelphia defense lawyer Jeffrey Lindy, a former federal prosecutor in Philadelphia and former assistant state prosecutor in Brooklyn, N.Y., who has handled arson prosecutions, said "a murder-suicide by arson would be highly unusual. I would put that at the very bottom of my list."

Lindy, who has no connection to the Sheridan case, said the absence of a weapon that caused John Sheridan's wounds was also problematic for a murder-suicide ruling and more indicative of an intruder who left with the weapon. However, he said, investigators may have more information than has been revealed publicly.

L. George Parry, a Philadelphia defense lawyer and former federal prosecutor, agreed information about the arson and an unrecovered weapon were "very, very strong indications that this was a double homicide."

"I wouldn't expect a person intent on committing suicide to set a fire at the scene," said Parry, who also has no involvement in the case. "You usually see that kind of action being taken by someone who wants to destroy the crime scene, to impede any investigation."

One source familiar with the investigation said that although authorities first suspected murder-suicide, they did not rule out the possibility both Sheridans were murdered.

Sheridan relatives had serious doubts the couple's relationship, bound by 47 years of marriage, would end in a deadly domestic battle, Mitchko said. There were no obvious marital or financial problems, he said. At a memorial service for the Sheridans, their sons recalled their parents as a happy couple who loved each other.

After the Sheridans' deaths, the family immediately hired Michael Baden, a nationally renowned forensic pathologist, to provide his own analysis.

Joyce Sheridan, 69, was a retired history teacher. John Sheridan, 72, who served as state transportation commissioner in Gov. Thomas Kean's administration, was a Republican insider who helped shape public policy.

John Sheridan, whose manner of death is listed as "pending investigation" on his death certificate, had multiple wounds, including one on his neck that nicked his jugular vein and that apparently was caused by a weapon with a rounded edge, Mitchko said. He was pronounced dead at the scene.

Mitchko said Baden, who examined John Sheridan's body, found the neck wound. The state medical examiner who performed autopsies had not included the neck wound in an initial report but concurred with Baden's findings, Mitchko said.

Mitchko, a retired government bank examiner, said that he spoke with Baden early in the case and that the pathologist suggested there was carbon monoxide in John Sheridan's blood.

Baden, reached at his home in New York City, declined to comment, saying he could discuss the findings only with the Sheridan family's permission.

Joyce Sheridan was stabbed repeatedly in the upper body, Mitchko said. She was pronounced dead at a local hospital. Her death was ruled a homicide, according to her death certificate, which does not list a cause.

A gas can usually kept in the garage also was found in the bedroom, sources said. Two sources familiar with the probe said detectives had recovered two knives.

Mitchko said he was told that in addition to a steak knife used on Joyce Sheridan, a serrated bread knife was found at the scene. Neither of those knives caused John Sheridan's wounds, two sources familiar with the investigation said.

The unrecovered weapon or weapons may explain why authorities have released so little information about the case.

Capt. Jack Bennett, a spokesman for the Somerset County Prosecutor's Office, e-mailed reporters in early October that his office was awaiting additional lab analyses. He would not estimate how long it would take to complete those tests, or which analyses were underway.

Legal experts say that the lab tests likely have been completed but that the results might have left investigators still searching for answers.

The possibility of a third weapon throws a monkey wrench into the investigation, said Glenn Zeitz, a Moorestown lawyer not involved in the case. "It creates the potential issue of a third party. That stopped them in their tracks."

Lawyers and investigators with the New Jersey Attorney General's Office and state police detectives were dispatched last month to assist with the case.

Early in the investigation, Somerset County officials said there was no threat to the public. They said the Sheridans' sons - Mark, Matthew, Dan, and Tim - played no role in their parents' deaths.

Matthew Sheridan, 40, was arrested and accused of possession of cocaine and drug paraphernalia on the day his parents died. Bennett confirmed the arrest and said it was unrelated to the Sheridans' deaths. The Prosecutor's Office has not pursued charges against Matthew Sheridan but said it had up to five years to do so.

Contacted last week about the case, Bennett replied in an e-mail, "No updates."

Lee Vartan, a Manhattan criminal defense attorney for Holland & Knight and formerly with the state Attorney General's Office, said he could not comment on the specifics of the Sheridan investigation. In general, he said, authorities are reluctant to speak about a case until it's fully investigated.

"I think that's why it may appear to the public that this investigation is taking so long," Vartan said. "Everyone wants to get it right."

Crimes involving arson are complex by nature, he said. There are conflicting missions of responding agencies. The fire must be stopped from spreading while rescue efforts are underway, which can impact evidence, Vartan said.

"The primary mission of firefighters is to put out the fire. Things may be moved," Vartan said. "If the fire burned hot enough, it absolutely could warp or destroy evidence, making it all the more difficult and complex to re-create the scene and piece together."

Zeitz agreed, adding: "At some point in time, they have to fish or cut bait. This won't go on indefinitely."

Editorial

Somerset County prosecutor's silence has produced nothing new, only speculation and suspicion. Currents, C4.

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