PORTLAND, Maine — A U.S. resident accused of mailing cyanide to a suicidal resident of England so he wouldn’t tell investigators he had been defrauded pleaded guilty Monday to some of the charges against him as his trial began.

Sidney Kilmartin changed his not-guilty plea on wire and mail fraud charges to guilty in federal court in Bangor. He pleaded not guilty to charges of mailing injurious articles resulting in death, witness tampering and witness retaliation, and his trial on those charges began later Monday with jury selection.

Investigators have said Kilmartin advertised and mailed a substance he claimed was cyanide to several suicidal people. The substance was actually Epsom salt.

But Kilmartin mailed the real thing to 49-year-old Andrew Denton, of Hull, England, to prevent him from telling investigators about the fraud, investigators have said. Denton then killed himself.

“With respect to Mr. Denton, the government has further alleged that after Mr. Denton filed a complaint against Mr. Kilmartin for mailing him Epsom salts, Mr. Kilmartin sent him actual potassium cyanide, which Mr. Denton used to kill himself,” court records state.

Kilmartin had moved to stop the government from using Denton’s emails as part of the trial, but the court ruled the emails are admissible.

Court records also show that the government intends to bring more than 30 witnesses to speak in the trial. The witness list includes people Kilmartin is accused of defrauding through the mail, representatives for police and public safety departments in England, and a toxicologist for the FBI.

An affidavit by a U.S. postal inspector said Kilmartin obtained the highly toxic cyanide by posing as a jeweler to persuade a California distributor to ship him 100 grams of the industrial-grade chemical for $127.56.

A spokesman for the federal prosecutor’s office declined to comment on the case, which is expected to last several days.

A defense attorney for Kilmartin did not return a phone call seeking comment on the case. Kilmartin previously lived in Windham, a town of 17,000 outside Portland.