Details unfold in a disturbing case linking a US woman's murder of her estranged husband to her South African lover's attempt to hire hitmen before acquiring a lethal tranquilliser.

A failed appeal against their sentences by two US women convicted of a 2022 murder using an animal tranquilliser has unmasked further details about the case's South African links.

Amanda Hovanec was in a romantic relationship with Anthony Theodorou, of Pretoria, who, according to a US court finding last week, approached three potential hitmen in South Africa for her.

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The third provided Theodorou with the powerful animal tranquilliser etorphine, which he shipped to the US at Hovanec's instruction.

On April 24, 2022, Amanda Hovanec injected her estranged husband, Timothy Hovanec, with the etorphine.

(Timothy Hovanec will now be referred to by his first name so as not to confuse him with his wife.)

'1,000 times more potent than morphine'

Also known as M99, etorphine, used to immobilise large, wild animals, is strictly regulated. Poachers are known to use it on rhinos.

US authorities said, "The investigation determined that the victim was injected with M99... [a] controlled substance approximately 1,000 times more potent than morphine...

"According to court records, Hovanec considered killing her husband for at least a year before the murder and had considered alternate means to do so, including hiring a hitman, before settling on injecting him with...