Sidney P. Kilmartin advertised himself as a dealer of death, offering potassium cyanide online as “a painless and quick way to commit suicide” to anyone who could pay $250 a gram.

Posing as a jeweler, the Windham man convinced a California distributor to ship him 100 grams of the industrial-grade chemical for just $127.56.

And he wrote an email to a suicidal customer in England with some advice: “You definitely want to take this on an empty stomach.”

Those accusations against Kilmartin came out Friday when a judge’s seal on search warrant documents was lifted in U.S. District Court in Bangor. Investigators from the U.S. Postal Inspection Service used that search warrant to obtain copies of emails between Kilmartin and a man he allegedly helped kill in England.

The records were unsealed a little more than a month before Kilmartin, 52, is scheduled to stand trial on charges of mailing cyanide and mailing cyanide resulting in the death of Andrew Denton, a depressed 49-year-old man in Hull, England, who was found dead on Dec. 31, 2012.

Kilmartin, who has a history of mental illness, is accused of sending two batches of cyanide to Denton in 2012. The first batch, sent on Nov. 16, failed to kill Denton. But the second batch, which investigators say Kilmartin sent by U.S. mail on Dec. 11, worked.

Denton was found dead with 17 milligrams of cyanide per liter in his blood – more than three times the lethal dose of 5 milligrams per liter, according to Humberside police in England.

Denton had left a message on his own voice mail that said, “Expect the worst,” U.S. Postal Inspector Michael Desrosiers wrote in the newly unsealed affidavit in support of a search warrant.

Kilmartin’s case is scheduled for jury selection on April 7, with a tentative trial date for that day or thereafter. If convicted, he faces up to life in prison. Though the more serious of the two charges against Kilmartin can carry a death penalty, prosecutors are not seeking it.

Kilmartin has pleaded not guilty to the charges and has remained in federal custody since his arrest Nov. 5 following an indictment.

Kingston-upon-Hull, often abbreviated as Hull, is a city of more than 250,000 about 200 miles north of London.

Denton had spent years struggling with depression before his death and had made multiple suicide attempts before taking the fatal dose of cyanide, according to an article last year in the Hull Daily Mail.

Potassium cyanide is a highly toxic, colorless salt, similar in appearance to sugar, according to the U.S. Centers for Disease Control and Prevention. Used commercially for fumigation, electroplating and extracting gold and silver from ores, it is usually shipped as capsules, tablets or pellets. It releases highly toxic hydrogen cyanide gas, which interferes with the body’s ability to use oxygen. Swallowing the chemical causes nausea, vomiting, abdominal pain and irritation or corrosion of the lining of the esophagus and stomach. Ingestion can quickly result in death.