CINCINNATI -- A man accused of posing as a doctor who rode with Cincinnati paramedics and declared a man dead has a long history of mental illness, according to his brother.

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John Holliman, 20, is charged with three counts of practicing medicine without a certificate or surgery without certificate and one count of disrupting public service, WLWT Eyewitness News 5 reported. If convicted, Holliman faces up to 4.5 years in prison.

Posing as Dr. Antoine Douglas of Lexington, Ky., Holliman allegedly rode with Cincinnati paramedics on three days: June 2, 15 and 29. He may have ridden with the paramedics for as long as 27 days, WLWT reported.

On June 29, Holliman responded with paramedics to the Hamilton County Justice Center, according to investigators, where witnesses said inmate Walter Malachi was either dead or dying. Investigators said Holliman pronounced Malachi dead, ordering paramedics to, "Mark the time, 10:36. I'm pronouncing him dead."

Holliman has never received medical training, WLWT reported, and Cincinnati fire officials said Holliman did not touch any patients or administer medical care.

John Holliman's brother, Rashaun Holliman, said John is a brilliant person with a history of mental illness.

"John has been in and out of institutions since the age of 8," Rashaun Holliman said. "He's been in over 12 institutions all the way from Dayton to St. Louis. Some of the diagnosis he's received, they've said he's schizophrenic, he's bi-polar."

While in those intuitions, John Holliman was read books on medicine and anatomy, his brother said.

"He's always been fascinated with fire trucks and police squads, stuff like that," Rashaun Holliman said.

The reading allowed Holliman to allegedly pose a doctor and a police officer in several cities, including Lexington, Ky.

"He struck me as very intelligent, that he could very easily have been a doctor," Lexington Paramedic Mark Harvey said. "He knew all the inside lingo and knew different medications and medical conditions of patients."

In Columbus, John Holliman has been arrested for impersonating a police officer and inducing panic. He was released from prison in April, Rashaun Holliman said.

"For this time, I believe he was in there for falsification," Rashaun Holliman said. "I think that what he was doing was portraying himself to be a dispatcher with the 911 department here in Columbus, and I believe that he called out Med Flight to our home in Pickerington."

Family members said they are saddened to see a brilliant mind used improperly.

"That's the really sad part about this," Rashaun Holliman said. "His life seems to be wasted and put from one criminal facility to another instead of getting the help he needs."

Stay tuned to WLWT Eyewitness News 5 and ChannelCincinnati.com for news updates around-the-clock.