BANGOR, Maine (NEWS CENTER) -- A Windham man accused of mailing cyanide to a suicidal man in England who killed himself is pleading not guilty to the six charges against him relating to the death.

54-year-old Sidney Kilmartin pleaded guilty to nine federal charges of mail and wire charges but not to the federal charges relating to the death of Englishman Andrew Denton. Those charges include mailing injurious articles resulting in death, wire fraud, mail fraud, witness tampering and witness retaliation relating to the

Investigators say Kilmartin advertised and mailed a substance he claimed was cyanide to several suicidal people. The substance was actually Epsom salt, the AP reports.

It also reports that prosecutors say Kilmartin mailed the real thing to 49-year-old Andrew Denton of Hull, England, to keep him from telling investigators about the fraud. Denton then used the cyanide to commit suicide.

If found guilty of the remaining six crimes, Kilmartin could face a maximum of life in prison.

Kilmartin has a history of mental illness and was previously committed to a psychiatric facility in 2008.