COBB COUNTY, Ga. — A convicted rapist and confessed serial killer says his two decades of murders started in Cobb County - when he was only 12 years old.

11Alive has confirmed that multiple law enforcement agencies in Georgia are investigating Nicholas Gibson's claims.

Gibson told investigators he killed a homeless man in a wooded area of Cobb County in 1999. It would be the first of at least seven alleged murders across the country.

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A year later, at the age of 13, Gibson was convicted of rape. He spent seven years at a juvenile facility in Illinois.

Authorities say he murdered a 77-year-old man with a sword in south Florida before escaping to New York - and then getting caught earlier this month.

Nicholas Brent Gibson
Nicholas Brent Gibson
Georgia Department of Transportation

Gibson is the prime suspect in the grisly murder of 77-year-old Erik Stocker, whose decomposing, mutilated corpse was found in Miami Beach 10 days after investigators believe he was killed.

When asked by a reporter if he committed the murder, Gibson mouthed "with my bare hands."

He also said "yes" when asked if he committed his first murder at age 12.

Gibson was convicted of aggravated sexual assault in Illinois as a juvenile in 2000 and spent seven years in a juvenile prison having been placed on the sex offender registry at that time.

Months later, he was allegedly picked up in Pennsylvania on several sexual assault charges and spent another four years and six months behind bars.

Three months later, Gibson ended up in Cobb County, Georgia where state records show he spent more time behind bars at Dooly State Prison.

He skipped bond and disappeared before resurfacing in Miami Beach in 2013, facing arrests for trespassing and failure to register once again. He ended up being sent back to Georgia where he did two more years of prison after failing to register as a sex offender again.

He ended up back in Florida and eventually back in prison before being released again in late 2018. Less than a year later, he's now accused in Stocker's death.

It was during his most recent arrest that police said he admitted that there were more murders in his troubled history - six across Florida, Georgia, and California. But authorities are still trying to determine if this is true.