US serial killer Todd Kohlhepp has written a letter claiming he killed more than the seven people he has been convicted of killing.
The letter consists of eight pages and claims this is not the first time he has tried to admit to more criminal acts.
He sent the letter to the Herald-Journal in South Carolina and it said "yes there is more than seven."
The 46-year-old claimed: "I tried to tell investigators and I did tell FBI, but it was blown off.
"It's not an addition problem, it's a multiplication problem. Leaves the state and leaves the country. Thank you private pilot's license."
Chief division counsel with the FBI's Columbia office, Don Wood, said there is a pending investigation but commented no further, The Associated Press reported.
Kohlhepp appeared in court in May and pleaded guilty to seven counts of murder. He was given seven consecutive life sentences and will not be entitled to parole.
Due to pleading guilty the prosecution agreed not to call for the death penalty, according to ABC News.
The man was arrested last year following the discovery of a woman chained up at his property, she told police that Kohlhepp had killed her boyfriend and his body was then discovered in a shallow grave, also on the the killer's property.
This led to his admission of six other killings which took place during more than 10 years.