Experts say the injury can be associated with suicide or strangulation.
Epstein had pleaded not guilty in July to charges of sex trafficking involving dozens of underage girls between 2002 and 2005.
"The victims will regrettably never see Mr. Epstein brought to justice, and unless one of his accomplices is charged, they may never see a public trial that establishes the abuse they suffered", he continued.
The Federal Bureau of Prisons, which runs the Metropolitan Correctional Centre in lower Manhattan where Epstein was jailed, said there had not been an inmate suicide there since 2006.
Epstein's family hired its own pathologist, Michael Baden, who was present during the autopsy, according to the source, and he is also not disputing preliminary findings from the medical examiner that Epstein killed himself.
Guards were supposed to check Epstein every thirty minutes as per protocol, but video footages show that two guards who were assigned to him were sleeping at times and didn't go up to his unit for nearly three hours.
Epstein, 66, who once counted Republican President Donald Trump and Democratic former President Bill Clinton as friends, was found unresponsive in his cell on Saturday morning, according to the Federal Bureau of Prisons. Yet after he reportedly spoke of warning Epstein about bad behavior and tried to help him avoid scrutiny from police, Zinoviev tried to retract earlier claims about Epstein's alleged relationships with teenage girls, calling them "a misunderstanding".
The age of the deceased is also important, Arden said.
While Attorney General William Barr has warned that Epstein's co-conspirators should not "rest easy" in the wake of his death, Maxwell - who would logically be next in line for prosecution, given her close involvement in the alleged trafficking as outlined in court documents - remains a free woman.
"It's unusual to have a neck fracture", Dr. Hua said.
Two weeks later, Sampson's office concluded the officer's actions were the primary cause of his death.