The body of notorious 1930s American gangster John Dillinger is expected to be exhumed in September from a concrete-encased grave at an Indianapolis cemetery more than 85 years after he was killed by FBI agents outside a Chicago theatre.

The upcoming exhumation could put to rest conspiracy theories suggesting that the violent criminal some people considered a folk hero during the height of the Great Depression isn’t even buried in his marked grave.

The Indiana State Department of Health approved a permit on July 3 sought by Dillinger’s nephew, Michael Thompson, to have the body exhumed from Crown Hill Cemetery and reinterred there.

The permit doesn’t give a reason for the request, and Mr Thompson couldn’t immediately be reached for comment. However, Dan Silberman of A&E Networks said the exhumation would be covered as part of a documentary on Dillinger for The History Channel.

Indiana health department spokeswoman Jeni O’Malley said based on the permit, the agency expects Dillinger’s body would be exhumed and reinterred on September 16 – the date listed on the document.

But digging up Dillinger’s grave might prove a difficult task because days after his son’s funeral, Dillinger’s father had the casket reburied under a protective cap of concrete and scrap iron topped by four reinforced-concrete slabs.

A photograph of Dillinger taken shortly before he was killled. Photo: Getty

The Indianapolis-born Dillinger was one of America’s most notorious criminals. The FBI says his gang killed 10 people as it pulled off a bloody string of bank robberies across the Midwest in the 1930s.

Dillinger was never convicted of murder. He was even considered a folk hero by some during his gang’s violent rise amid the Great Depression as banks were failing, others were limiting withdrawals and many Americans had lost homes and farms to foreclosure.

Dillinger was awaiting trial in the slaying of an East Chicago police officer when he escaped from jail in Crown Point, Indiana, in March 1934 with a gun carved out of wood. While on the run, he had plastic surgery to alter his face and was said to have tried to remove his fingerprints with acid.

Dillinger, who was portrayed by Johnny Depp in the 2009 movie Public Enemies, was fatally shot in July 1934 by FBI agents outside the Biograph theatre in Chicago after he was betrayed by a woman who became known in the papers as the Lady in Red.

Crown Hill Cemetery spokeswoman Crystal King said the cemetery has no information about the plans to exhume Dillinger, whose grave is an attraction at the hilltop graveyard on Indianapolis’ near north side.

-AAP