Case closed: Sidney Kilmartin, 56, was sentenced on Tuesday to 25 years in prison for mailing a fatal dose of cyanide to a suicidal Englishman in 2012

A Maine man was sentenced on Tuesday to 25 years in prison for mailing a fatal dose of cyanide to a suicidal Englishman, which the victim used to end his own life.

Sidney Kilmartin, 56, learned his fate four years after he was arrested for sending the poison to Andrew Denton of Hull, England.

The case raised several legal questions, including whether the act of mailing a fatal substance to a suicidal person was tantamount to murder.

The Windham, Maine, resident, was found guilty in 2016 of mailing injurious articles resulting in death and witness tampering in a case that frequently was delayed in court. His lawyer, Bruce Merrill of Portland, said he would appeal both the conviction and the sentence.

Investigators charged Kilmartin with advertising and mailing a substance he said was cyanide to several suicidal people. It was really Epsom salt.

But the investigators found Kilmartin sent the real thing to Denton after Denton had threatened to report the fraud, and the Englishman used it to kill himself on New Year's Eve in 2012. He was 49 years old.

A court affidavit said Kilmartin obtained the cyanide by posing as a jeweler to persuade a California distributor to ship him 100g of the lethal chemical for $127.56.

Andrew Denton (pictured), 49, took the cyanide and was found dead in his Hull, England, home on New Year's Eve in 2012

Judge John Woodcock expressed sympathy for Kilmartin, who himself has attempted suicide in the past, once intentionally overdosing on antipsychotic medication and drinking antifreeze.

But the judge added that Kilmartin's fraud and role in Denton's death represented an 'appalling moral vacuum' worthy of stiff punishment.

'Not merely illegal - they were perpetrated in a moral black hole,' Woodcock said. 'Just an unimaginable moral black well that these actions took place in.'

Kilmartin, who wore an orange prison jumpsuit and spoke only to address the judge, faced a maximum sentence of life in prison. Merrill had said in an earlier sentence hearing that he felt a fair sentence would range from zero to 20 years because of Kilmartin's history of mental illness.

ilmartin obtained the cyanide by posing as a jeweler to persuade a California distributor to ship him 100g of the lethal chemical (stock photo)

Kilmartin and Denton were 'kindred spirits' who related to each other because they were both suicidal, Merrill said Tuesday.

He said the two communicated in a chatroom about the most effective way to take the cyanide, a highly toxic, colorless salt.

'Two very ill, depressed people talking about the best way to take potassium cyanide,' he said. 'Not the kind of conversation people normally have.'

US Attorney Halsey Frank said during Tuesday's sentencing that Kilmartin deliberately took advantage of depressed people for his own gain. He described Kilmartin's actions as 'killing someone to obstruct justice while taking advantage of vulnerable people.'