Seven years after John and Joyce Sheridan were found stabbed to death in their New Jersey home, one of their sons has asked prosecutors to investigate his parents’ deaths in light of an “eerily similar” murder-for-hire plot revealed this week in federal court in Newark.

In a letter Friday to county and state prosecutors, Mark Sheridan urged them to compare a knife seized from an alleged participant in the North Jersey plot to see if it matches one missing from his parents’ home in the highly publicized and perplexing case.

John Sheridan Jr. , the chief executive of Camden’s Cooper University Health System, and his wife were found fatally stabbed in their home, which had been set on fire. Authorities initially concluded that their deaths were a murder-suicide -- a finding that their four sons have vehemently questioned.

» READ MORE: Sheridan investigation documents detail final days and crime probe

Mark Sheridan wrote that “your offices all but laughed at my family’s suggestion that my parents’ deaths were anything other than a murder-suicide. Indeed, both offices openly mocked the idea of a killing for hire involving a stabbing with a fire set to destroy evidence.”

He noted that earlier this week, a North Jersey political consultant and a Philadelphia man pleaded guilty to just such a scheme, one in which the victim was fatally stabbed and his apartment set on fire. The fatal attack took place in May 2014, four months before the Sheridans’ deaths. But alleged culprits were only named this week with guilty pleas.

The guilty pleas were entered on Tuesday and Wednesday by Sean Caddle, 44, who has been a consultant for Democratic Party candidates, and Philadelphian Bomani Africa. In a hearing this week, federal authorities said Caddle hired a conspirator in Connecticut, George Bratsenis, to kill an associate of Caddle’s and that the conspirator recruited Africa to help. They said Bratsenis and Africa went to the target’s residence in Jersey City and killed him and set his apartment on fire.

According to NJ.com, authorities have not charged Bratsenis. Prosecutors have not named the victim, but said the fatal stabbing occurred on May 22, 2014. On that same date, however, Michael L. Galdieri, 52, who also worked in politics and was the son of the late Democratic State Sen. James A. Galdieri, was fatally stabbed in an apartment that was then torched, news accounts show.

Africa, 61, and Bratsenis, 73, were both indicted and pleaded guilty in a federal case stemming from a bank robbery in Connecticut in September 2014. Prosecutors in that case alleged a “long-blade butcher’s knife” was found in the white pickup truck that Bratsenis was driving at the time of his arrest on Sept. 29, 2014, court records show.

The Trumbull Times also reported a long kitchen knife was allegedly recovered in the vehicle, in a story published soon after Bratsenis was arrested.

In his letter Friday, Mark Sheridan referenced media reporting on the knife. He went on to say the Somerset prosecutor’s office had “inquired of my brothers and me multiple times regarding a knife that was missing from the knife block in the kitchen” after his parents died.

The son sent the letter to Somerset County Prosecutor Michael Robertson and Andrew Bruck, the acting attorney general for New Jersey. Sheridan noted that neither man was the top prosecutor when his parents died. U.S. Attorney Phillip Sellinger in Newark was also copied on the letter.

He asked the New Jersey officials to reach out to federal prosecutors in Connecticut who are pursuing the criminal case against Bratsenis in the robbery to obtain “photos of the knife recovered at the time of his arrest to determine if it matches the set of knives from my parents’ kitchen.”

Sheridan also asked officials to obtain a DNA sample from the knife.

The U.S. Attorney’s office in New Jersey and the state Attorney General’s office had no comment on Sheridan’s letter. The Somerset County prosecutor’s office did not immediately respond to requests for comment.

An attorney for Bratsenis in the Connecticut bank robbery case did not immediately respond to messages seeking comment and could not be reached by phone at his office. Court records show Bratsenis has been in prison while awaiting sentencing in the robbery.

Sheridan, 72, led Cooper hospital from 2008 until his death. A prominent Republican, he served as state transportation commissioner for GOP Gov. Thomas H. Kean Sr. in the early 1980s and worked on transition teams for Govs. Chris Christie and Christie Whitman. His wife, 69, was a retired schoolteacher.

The Sheridans were found dead in the master bedroom of their home in Skillman, seven miles north of Princeton, on Sept. 28, 2014. Each had been stabbed multiple times and suffered burns from a fire intentionally set in the room. John Sheridan also had five broken ribs and a chipped front tooth. Sheridan’s body was found beneath a burning two-piece armoire dresser.

State authorities initially concluded in 2015 that John Sheridan stabbed his wife and then set fire to their bedroom.

Their four sons hired an independent forensic pathologist who disputed those findings, saying none of the knives found at their house caused John Sheridan’s narrow wounds. In addition, renowned pathologist Michael Baden concluded that DNA found on a bloody knife in the bedroom matched that of a male, but not the genetic profiles of Sheridan or his sons. Baden wrote in an affidavit that John Sheridan’s other wounds were signs of an attack.

Baden, a former chief medical examiner in New York City, concluded the Sheridans were likely slain by an intruder who set the fire in an attempt to destroy evidence.

The Sheridan sons sued to have their father’s death certificate changed, and in 2017 the state medical examiner’s office changed his manner of death from suicide to undetermined. In his report, New Jersey Medical Examiner Andrew Falzon wrote that the weapon that caused Sheridan’s five stab wounds had not been recovered.

But authorities would not say at the time whether they planned to reopen the investigation, though many outside experts encouraged them to do so.