Three former New Jersey governors are among those calling for a new investigation into the deaths of Cooper Health System CEO John P. Sheridan Jr. and his wife, Joyce, and to change John Sheridan's manner of death from suicide to undetermined.

Former Gov. Christie Whitman said Wednesday that she believes that the Sheridans may have been murdered and that the state should reopen the investigation.

Whitman and nearly 200 others, including more than 40 members of Sheridan's former law firm, Riker, Danzig, Scherer Hyland & Perretti, signed an open letter released Wednesday as being from "Friends of John and Joyce Sheridan."

When asked whether she believed John Sheridan was murdered in September 2014, Whitman responded: "I believe that is a distinct possibility. I don't know how else to explain what happened."

Whitman said she and "those of us who knew him . . . just find this [the judgment of murder-suicide] extraordinarily hard to believe. It is not the kind of action one would associate with him." She added that the case "warrants a further examination."

The one-page letter supports the efforts of the Sheridans' four sons. It also includes the names of former Govs. James J. Florio and Thomas H. Kean, along with other prominent New Jersey political and business leaders and Sheridan family friends. They include Cooper's board chairman, George E. Norcross III; former New Jersey Supreme Court Justice Gary Stein; former state Attorneys General John J. Farmer Jr. and Peter C. Harvey; and Ed Stier, former director of the state's Division of Criminal Justice.

Stier, who knew John Sheridan, said Wednesday that he had watched the case closely and had "given a lot of thought" to the investigation. "There is significant evidence to show that John Sheridan was murdered," he said.

Although it would be difficult to investigate after evidence has been compromised, Stier said, it is not impossible, adding that he believes the attorney general's Division of Criminal Justice should reopen the case. Stier said the division had an obligation to investigate when it became clear local authorities were not looking for suspects.

"The [Somerset County] Prosecutor's Office completely blew the crime-scene investigation," Stier said, adding that evidence was not properly collected during a "sloppy" investigation, and that the murder-suicide ruling came prematurely. "This is absolutely the wrong way to go about an investigation," he said.

The governor's office referred questions to the Attorney General's Office. Peter Aseltine, a spokesman for the acting attorney general, declined to comment.

Wednesday's letter refers to both deaths as murders, but provides no new information to support the claim. "The only truth in this terrible tragedy is that no one knows what happened on that September morning - not us, not the medical examiner, not the prosecutor," the letter says.

"But most of all we believe that John Sheridan - through his personal and professional life in New Jersey - earned the right to have his life and death assessed competently and accurately."

In March 2015, after a six-month investigation, Prosecutor Geoffrey Soriano and state Medical Examiner Eddy Lilavois concluded the deaths were a murder-suicide.

Soriano declined to comment Wednesday, writing to the Inquirer: "In light of the fact that the Sheridan family is currently pursuing action to challenge the medical examiner's determination as to the manner of the death of John Sheridan, it is my firm belief that it would be inappropriate for me to provide any comment on this matter."

John and Joyce Sheridan were found Sept. 28, 2014, unresponsive in the second-floor bedroom of their Montgomery Township home. The Somerset County prosecutor concluded that John Sheridan fatally stabbed his wife, stabbed himself five times, and set their master bedroom on fire.

Wednesday's letter was written by Jim Weinstein, New Jersey's former transportation commissioner, and Dennis Culnan, a public relations consultant.

Weinstein also served with the transportation agency under John Sheridan, who was appointed transportation commissioner by Kean in 1982.

Dan Sheridan, one of the couple's sons, said in a statement that the siblings appreciated the support.

"The willingness of so many to join us and publicly speak out about the need to reopen the investigation into our parents' deaths gives us hope that eventually we will find out who killed our parents," Sheridan said.

Weinstein said he believes the Sheridans were murdered by an intruder or intruders. He said he began gathering support for the couple's sons about six months ago.

"There's no way anyone who knew John, and knew and worked with him, believes John could have done this. It's just not who John was," Weinstein said. "We loved both of them and they deserved better than this."

Weinstein said the group members decided to write an open letter, rather than addressing it to a person or agency, because they did not want to limit who could or would respond.

The deaths stunned many in the political and social circles where the couple was known. Friends, relatives, and neighbors have said that it seemed unlikely that Sheridan, described as mild-mannered, would kill his wife of 47 years. Somerset County investigators found no signs of mental illness or troubles in the Sheridans' marriage. Authorities suggested John Sheridan might have snapped because of work pressures.

All three former governors and Gov. Christie attended a memorial service for the Sheridans in October 2014, speaking fondly of the couple, their love for each other, and their dedication to public service.

Although Joyce Sheridan, a retired schoolteacher, stayed away from politics, she often prodded her husband to encourage politicians to work faster.

In March, as Somerset County investigators were finishing their investigation, a public battle erupted when the couple's sons - Dan, Tim, Matt, and Mark, a lawyer for Squire Patton Boggs in Newark, N.J., and a former general counsel for the state's GOP - alleged that authorities had prematurely concluded that the deaths were murder-suicide, and had closed the case to cover up incompetence by investigators and a state medical examiner.

In April, the Sheridan family said it would pay a $250,000 reward for information that identified the person(s) responsible for their parents' deaths.

Wednesday's letter comes as the family waits to hear whether the manner of death will be changed as requested in a Dec. 18 administrative petition to the New Jersey Office of the Medical Examiner; acting Attorney General John J. Hoffman, whose office oversees medical examiners; and prosecutors.

The petition included an affidavit from a nationally known forensic pathologist, Michael Baden, who conducted a second autopsy on John Sheridan after he was hired by the family days after the deaths.

Baden discovered that the weapon that caused John Sheridan's stab wounds had not been recovered and, according to the family, also concluded that John Sheridan's death was more likely a homicide.

Experts who reviewed evidence and information for the Inquirer in October 2015 agreed that John Sheridan's death was more likely a homicide, and that the investigation was closed prematurely.

"We have long agreed with independent experts and the media that have reviewed the case that there are compelling reasons to question the murder/suicide conclusion reached by the medical examiner and the Prosecutor's Office," according to the letter.

The letter noted the issues surrounding a "flawed" investigation raised recently in the Inquirer and the New York Times, as well as earlier stories, including in the Newark Star-Ledger.

If state authorities refuse to change the manner of John Sheridan's death, Mark Sheridan has said, the family will pursue legal action.