A Kiwi euthanasia advocate now faces a second charge of murdering a disabled person.

According to the BBC, Sean Davison appeared in the Cape Town Magistrate's Court on Friday on two counts of murder. Charges he denies.

The 75-year-old forensic scientist founded the right-to-die organisation DignitySA.

Davison is now accused of killing Justin Varian by placing a bag over his head and administering helium, the BBC reports.

Varian died on July 25, 2015. He had been diagnosed with motor neurone disease some years prior.

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Davison was already charged in relation to the death of friend Anrich Burger, 43, on November 2, 2013.

Burger had become a quadriplegic after a car accident.

Auckland-born Davison moved to South Africa in the early 1990s and went on to become a professor of biotechnology at the University of the Western Cape.

Davison previously made headlines in New Zealand when he was convicted in relation to the death of his 85-year-old mother, who had terminal cancer.

Archbishop Desmond Tutu wrote to the judge asking for leniency, and gave Davison a character reference, the BBC reports.

Davison served five months' of home detention after pleading guilty to assisting his mother's suicide, before he returned to South Africa in 2012.

He is currently on bail, and is due to appear again in court on January 29.

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