Dan Rivera, a 54-year-old paranormal investigator and US Army veteran, died suddenly on Sunday while touring with the allegedly haunted Annabelle doll in Pennsylvania.

Rivera was in Gettysburg as part of his sold-out “Devils on the Run Tour” when emergency services were rushed to his hotel room, according to the Evening Sun.

Despite attempts to revive him with CPR, Rivera was pronounced dead shortly after.

He was reportedly found alone in his hotel room.

The coroner’s office stated that Rivera’s death did not appear suspicious. His exact cause of death remains unclear and an investigation is ongoing.

His death was announced on Monday by the New England Society for Psychic Research (NESPR), the organisation founded by famed paranormal enthusiasts Ed and Lorraine Warren, who came into possession of the Annabelle doll in the 1970s.

Rivera had served as the lead investigator with NESPR for over a decade.

“Dan was not only a vital part of our team for over a decade, but also a deeply compassionate, loyal and dedicated friend,” the group said in a statement.

Born and raised in Bridgeport, Rivera reportedly encountered “haunting phenomena” early in life, having witnessed paranormal events in his childhood home.

A biography on NESPR’s website describes him as an expert “in the rites and rituals of Santeria.”

Rivera had become a prominent face in the paranormal community, appearing on the Travel Channel’s “Most Haunted Places” and serving as a producer for Netflix’s “28 Days Haunted”.

As part of the tour, Rivera and NESPR members travelled across the U.S. to display the Annabelle doll, which has long been at the centre of chilling folklore.

The doll, originally gifted to a Hartford nurse in the 1970s, allegedly began to move on its own and reportedly attacked someone.

The Warrens claimed it was possessed by an outside entity and took it into their care following an exorcism of the nurse’s apartment.

Rivera is survived by his wife Sarah and their four children.