Four members of the assisted suicide group Final Exit pleaded not guilty in Georgia Thursday to charges they ran an illegal organization that helped people die.

The indictment came a year after the suspects were arrested for allegedly assisting John Celmer, 58, die by breathing helium pumped into a plastic hood over his head. They also allegedly helped plan the suicide of an undercover state investigator who led them to believe he had pancreatic cancer.

If convicted, they could be sent to prison for up to five years on the suicide assistance cont, 10 years on the evidence tampering count and up to 20 years for racketeering.