Arrested without charge, she was accused of aiding the conspiracy that assassinated Lincoln and rapidly tried in a military court despite her civilian status. During this trial she was deprived of the right to testify on her own behalf and was afforded no right to an appeal. As the Daily Beast review summarized it:
The nation had never executed a woman, and until Surratt heads to the gallows, Aiken [the protagonist Union army veteran-turned-defense-attorney] thought he could save her. But the heavily bearded Civil War generals who acted as judge and jury never had any intention of sparing her. And even though Aiken succeeds in getting her a writ of habeas corpus, insuring a new trial by her peers, President Andrew Johnson, Lincoln’s successor, overturns it, and she dies along with the other conspirators.
“What is happening to Mary Surratt is an abomination. You have predetermined her fate,” Aiken tells Secretary of War Edwin Stanton (Kevin Kline). “Fine words for rallying a nation,” Stanton replies, “not for governing and keeping a nation together. Someone must be held accountable.”
While serving in the Boer War in South Africa, Morant likely summarily executed several Boer prisoners in retaliation for the killing of one of his comrades in the elite Bushveldt Carbineers, an irregular unit tasked with countering the guerilla tactics being used by the Boers.
The movie, one of the best courtroom dramas in my opinion, recounts the machinations of the British command to ensure that Morant and his comrades in the Bushveldt Carabineers were executed in order to conceal the fact that the British commander in South Africa, Lord Kitchener, had himself issued a "take no prisoners" order, and to appease the Germans with whom the English were hoping to reach a peace settlement.
The case is still very much in the Australian consciousness, especially in light of a recent discovery that appears to prove that British commander did in fact issue a "take no prisoners" order, which would undermine the entire basis of the Morant prosecution; the English, unsurprisingly, are unmoved by the new evidence: