PORTLAND — The federal government’s case against a Maine man charged with mailing cyanide to a suicidal Englishman has ground to a halt because of an overdue mental health evaluation.

An attorney for Sidney Kilmartin, of Windham, filed a notice of intent to use an insanity defense in March. Kilmartin has pleaded not guilty to charges of mailing cyanide that resulted in the death of Andrew Denton, a depressed 49-year-old man in Hull, England who was found dead in 2012.

The court hoped to have Kilmartin’s mental health evaluation by Aug. 7, Assistant U.S. Attorney Don Clark of the District of Maine said. The case will go back before Judge John A. Woodcock once the report is in hand.

But federal prosecutor Halsey Frank said the report has not arrived as of Wednesday. He declined to comment further on the case.

Kilmartin has a history of mental illness. He was previously committed to a psychiatric facility in 2008 after he was found not criminally responsible by reason of insanity for entering a man’s apartment and attacking him while he slept. He was released in 2011.

Frank said earlier in the case that Kilmartin was ordered held without bail because there was “no combination of conditions that would assure either his presence for trial” or the “safety of the community.”

Kilmartin faces a maximum of life in prison. English police have said Kilmartin and Denton exchanged emails and Kilmartin offered to sell Denton the cyanide, and also gave him advice about using it.

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

Clark said Kilmartin’s former attorney withdrew from the case on Aug. 4. The mental health evaluation is being conducted by the federal Bureau of Prisons, he said.

Kilmartin’s current attorney, Wayne Foote, said he is getting familiar with the case after picking up the files last week. He declined to comment further.

Potassium cyanide is a highly toxic salt that looks like sugar. Swallowing the substance causes nausea and vomiting and can swiftly kill a person.