A Windham man accused of mailing cyanide to a suicidal man in England who later used it to kill himself was indicted this week by a federal grand jury on several new charges that include witness tampering and witness retaliation.

Sidney P. Kilmartin, 53, remains incarcerated and was already facing two federal charges of mailing injurious articles to Andrew Denton of Kingston-upon-Hull, England. Denton used the cyanide to kill himself in late 2014.

Documents obtained from U.S. District Court in Portland on Thursday say that a new, superseding indictment, dated Wednesday, charges Kilmartin with one count of mailing injurious articles resulting in death, 12 counts of mail fraud and wire fraud, one count of witness tampering and one count of witness retaliation.

The indictment alleges that Kilmartin mailed the cyanide not to help Denton commit suicide, but as a means to prevent Denton from informing federal investigators about Kilmartin’s wire and mail fraud scheme.

Court records say that in 2012 Kilmartin advertised and mailed a substance he said was cyanide to at least four other people – it turned out to be Epsom salt. Denton and the four others sent money to Kilmartin after seeing an ad he had placed on a website devoted to people desiring to commit suicide. The ad claimed he had cyanide for sale.

Tests conducted by the Maine Health and Environmental Testing Lab determined the substance to be Epsom salt. Everyone who received a package in the mail survived, except Denton.

Kilmartin was arrested in November 2014. He is scheduled to go to trial in May and could face life in prison if convicted.