Anti-vaccine Dr Jeff Bradstreet was found dead in an apparent suicide in North Carolina after agents from the US Food and Drug Administration searched his office for reasons unknown.
The Rutherford County Sheriff's Office said in a news release issued this week that Bradstreet, 61, died of what appears to be a self-inflicted gunshot wound to the chest.
Bradstreet's body was found in the Rocky Broad River in Chimney Rock on June 19 by a fisherman and rescue team divers responded to the scene and recovered a handgun from the river.
Bradstreet ran the Bradstreet Wellness Center clinic in Buford, Georgia, and published autism research based on the disputed claim vaccines cause autism.
The medical community says such claims have been disproved.
The clinic was raided by agents from the FDA who were receiving assistance from the Georgia Drugs and Narcotics Agency, the Gwinnet Daily Post reported.
His family is raising funds online to investigate his death as some do not believe it was a suicide.
The investigator from the sheriff's office, Jamie Keever, said: 'I've talked to some of those people today.
'I don't know what to say. They have a right to their opinion.'
A GoFundMe page raising money to 'find the answers to the many questions leading up to the death of Dr Bradstreet, including an exhaustive investigation into the possibility of foul play' has already raised more than $15,000.
Fiona O'Leary of Autistic Rights Together [ART], responded to Bradstreet's death and the call for an investigation into his death.
She said: 'While it is very sad to hear of the death of Dr Bradstreet in such tragic circumstances, it is important to consider his position as one of the world's leading practitioners in the field of bio-medical treatments for autism.
'Many of these so called 'treatments' are unlicensed and unproven to be of any benefit to autistic people, indeed many can have serious and dangerous side effects on an individual's health and well being.
'Many supporters of Dr Bradstreet and the bio-medical industry are hailing him as a hero, claiming foul play at the hands of the government, yet the truth is more simple perhaps.
'None of the many so called treatments or cures could ever be substantiated and proven to be effective or beneficial outside of the bio-medicals own propaganda machine.'
Bradstreet's family is now raising funds online to investigate his death, including "an exhaustive investigation into the possibility of foul play."
The Bradstreet Wellness Center's website describes the practice's focus as "treating children with Autism Spectrum Disorder, PPD, and related neurological and developmental disorders," through the use of measured biomarkers.
"Our mission is to positively impact children's lives by meeting their biological, behavioral, and nutritional needs," it states. "Properly identify and address the underlying issues so that the child's brain, gut and immune systems can begin to function and heal."
In 2009, the U.S. Court of Federal Claims, Office of Special Masters found Bradstreet's research claiming causation between autism and environmental mercury exposure, which were published in non-peer-reviewed journals, and his testimony about links between a young patient's autism and his MMR vaccination, to be unconvincing and unsupported by evidence.
The court's opinion also questioned Bradstreet's treatment of a Florida boy whose family had filed a claim under the National Vaccine Injury Compensation Program. Over several years, Bradstreet prescribed a variety of dietary supplements, "de-yeasting," secretin infusions, immunoglobulin therapy and chelation therapy, as well as numerous non-standard laboratory tests which were not FDA-approved.