DENVER -- A couple who lost their 19-year-old son said they blame his death on a man who claimed to be a naturopathic doctor.

On Thursday, David and Laura Flanigan told state legislators their story with the hope of making it a requirement for naturopathic doctors to get licensed in the ongoing argument about conventional medicine versus alternative medicine and where the two overlap.

David and Laura Flanigan told lawmakers they didn't want others to go through their heartbreak.

As their son Sean was battling terminal cancer, they said they turned to alternative therapies.

"When you're told that your son is going to be saved, the thought of, 'Oh, how real can this be?' escapes you," David Flanigan said.

Brian O'Connell presented himself as a naturopathic doctor, though he had no real medical training.

He gave Sean a dangerous blood-cleansing treatment that only hastened his death.

O'Connell is now serving a 13-year prison sentence after admitting to criminal negligent homicide in the death of Flanigan.

"It's hard but we know we have to do it for Sean because he doesn't have a voice right now and we have to be that voice for him," Laura Flanigan said.

Lawmakers were shown phony diplomas in naturopathic health, a part, they said, of a growing problem.

But legitimate providers said the required licensing will only put them out of work.

"There are also countless traditional natural health care practitioners in good standing and work ethically to perform their duties in natural health and they want to help consumers," said naturopathic doctor Cheryl Strum.

The Flanigans said they believe in naturopathic medicine but that it needs to be better regulated. They said they thought they had checked O'Connell out. They said he had a wall full of diplomas, but it turned out they were all meaningless.