A U.S. suspect has pleaded not guilty to mailing cyanide to an Englishman who killed himself.

Federal investigators say Sidney Kilmartin of Windham, Maine, advertised and mailed a substance he claimed was cyanide to several suicidal people. The substance was actually Epsom salt.

But prosecutors say he mailed the real thing to Andrew Denton of Hull, England, to keep him from telling investigators about his moneymaking scheme. Denton, 49, used the cyanide to take his life.

Kilmartin pleaded not guilty Tuesday to federal charges of mailing injurious articles resulting in death, wire fraud, mail fraud, witness tampering and witness retaliation. He had previously pleaded not guilty to charges in Denton's suicide but those charges were superseded by the latest counts.

Kilmartin's attorney didn't immediately respond to a call seeking comment.