The man who believes that Charles Manson is his father wants to know the truth before the man who orchestrated a sseries of horrific killings dies in jail.

Matthew Roberts, 44 -- who says he was conceived at a San Francisco orgy attended by Manson in 1967 -- is worried that two inconclusive DNA tests were his last hope to confirm whether his father is the infamous cult leader, CNN's Miguel Marquez reports.

The new push for answers comes on the heels of 77-year-old Manson's latest parole hearing, which will likely be his last.

Roberts says that unless he sees "somebody scrape a piece of skin off [Manson's] ass and bring it to a lab," he can't be sure if Manson is his father, he told CNN.

Under California state law, inmates can be denied the chance to reapply for parole for up to 15 years. Another rejection after Wednesday's hearing makes Manson eligible again at 92, the Associated Press reported.

Roberts, whose mother put him up for adoption shortly after he was born, tried twice to confirm his true identity with DNA tests. But the results revealed that Manson's samples were contaminated. The New York Post reported that even Roberts' mother admits her son bears a striking resemblance to the incarcerated murderer.

"I didn't want to believe it," Roberts told the paper. "I was frightened and angry. I'm a peaceful person -- trapped in the face of a monster."

Manson is currently behind bars in Corcoran State Prison in Central California. Wednesday marked his 12th parole hearing -- he was denied and did not attend.

CORRECTION: An earlier version of this article listed Roberts' age as 41. He is 44. The article also described Charles Manson as a serial killer when actually he orchestrated a murder spree carried out by his followers in August 1969. We regret the error.