A South Carolina man who has already been convicted of killing seven people earlier this year has now confessed to murdering more, reports said.

Todd Kohlhepp, 46, was initially arrested after police searching for a missing couple found a woman, Kala Brown, chained inside a storage container on his property.

Brown told investigators that Kohlhepp had shot her boyfriend, 32-year-old Charles Carver, and kept her chained for two months.

Kohlhepp pleaded guilty in May to seven counts of murder for killings that took place over more than a decade, reports said.

Now, Kohlhepp has reportedly confessed to more killings in an eight-page letter to the Spartanburg Herald-Journal. 

Kohlhepp wrote that he told investigators and informed the FBI, but he said "it was blown off." He also wrote, "At this point, I really don't see reason to give numbers or locations." 

At the time of Kohlhepp's sentencing, his attorney told the court there were no other victims.

But in his letter, Kohlhepp wrote that his trail of murder "leaves the state and leaves the country,” the Herald-Journal reported.

Kohlhepp has already been sentenced to life in prison. 

Don Wood, chief division counsel with the FBI's Columbia office, told CBS News that the agency has a pending investigation.

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