SACRAMENTO (CBS13) – Retired FBI Agent Jeff Rinek knows how to get into the mind of a serial killer, and based on his conversation with Wesley Shermantine at San Quentin he believes the death row inmate sent CBS13 a letter to explain himself.

“He wants something and it’s my personal opinion that he seeks value,” Rinek said.

Value for a man isolated from the world, sitting in prison waiting to die and now gaining worldwide attention after mapping out for investigators a burial sites of victims.

Rinek says even serial killers like to feel good about themselves and Shermantine is no different.

“I try very hard to help them realize the value they have by giving closure to the families of the victims,” he said.

But in his letter addressed to CBS13 reporter Koula Gianulias, it’s clear Shermantine is a troubled man and has a strained relationship with his sister.

He writes “my dumb sister called and said I was suicidal.”

“I think he is making it very clear that his sister does not speak for him and does not have the ability to make decisions for him,” Rinek said.

But while Rinek can’t say for sure whether Shermantine is telling the truth in all his writings, he believes Shermantine wanted to help the family of one of his victims, Cyndi Vanderheiden, who went missing more than a decade ago…

Her whose remains are believed to have been found in Calaveras County last week.

“He knew that Mr. Vanderheiden was ill and he insisted that she be found and returned to him before he passed,” Rinek said Shermantine told him of his wish to give that family closure.

It’s not clear when Shermantine will speak out next. In his letter to CBS13, he says bounty hunter Leonard Padilla hasn’t paid him the $33,000 he has promised yet. He also says he’s never admitted to any killings but is the only one who knows of two additional burial sites now that fellow “Speed Freak Killers” accomplice Loren Herzog killed himself last month.