Sheridan family speaks exclusively to ABC News

Relatives of John and Joyce Sheridan are speaking out exclusively to ABC News, just days after the couple's deaths were ruled a murder-suicide.

The family says they are now working to clear John Sheridan's name.

The prominent political couple were discovered dead inside their burning home in an upscale New Jersey neighborhood.

The deaths of John and Joyce Sheridan back on September 28 seemed a mystery until now.

Investigators have declared it a murder-suicide and John Sheridan is now accused of fatally attacking his wife before setting their master bedroom on fire.

"They assumed it was a murder-suicide the second they walked on the scene," says the couple's son, Mark Sheridan.

This morning, in an ABC News exclusive, the Sheridans' family is fighting back, pointing out what they call gaping holes in the prosecutor's report - holes that point to a brutal double murder and a killer still at large.

"The community should be scared. The prosecutor had no idea what happened at that crime scene and he was out telling the public they were safe," says Sheridan.

The prosecutor's report concludes that the 72-year-old former political figure and hospital CEO used a kitchen knife to fatally stab his wife and used an unknown weapon to injure himself while also pouring gasoline on the floor and setting the fire that ultimately killed him.

Investigators say autopsies, interviews and even DNA evidence all point to one conclusion: murder-suicide.

"The prosecutor has indicted and convicted my brother of murder, when there hasn't even been a trial," said John's brother, Peter Sheridan.

The family has now released a list of unanswered questions, which they say are too many for the case to be closed.

Why were there no scratch marks on John Sheridan when DNA from an unknown source was found under the fingernails of Joyce Sheridan?

What was the motive? John Sheridan had been sending work emails just hours before the killings, even planning a meeting for the next day.

And the couple Face-Timed with their grandson that night with no signs of unrest.

Where is the weapon used to stab John Sheridan? Police never recovered it.

And what about the DNA on the knife used to kill Joyce?

"The DNA evidence in this case is extremely speculative," says Mark Sheridan.

The family is now planning to sue the prosecutor and other officials, not for money, but to clear John Sheridan's name.

"We're not gonna allow the prosecutor's office to destroy my father's legacy, my mother's legacy," says Sheridan.