A group of UN independent experts on Wednesday denounced the assassination of human rights advocate Zweli “Khabazela” Mkhize, and urged South Africa to hold perpetrators accountable.

The experts, referred to as the Special Procedures of the Human Rights Council, stated:

We urge South Africa to ensure a prompt, effective, impartial and thorough investigation into the killing and to take all necessary measures to hold those responsible accountable… Such heinous acts of violence constitute a direct assault on fundamental freedoms.

Civil society organizations, including the South African Human Rights Commission and the Socio-Economic Rights Institute of South Africa, backed UN demands.

Mkhize was a local leader and treasurer of Abahlali baseMjondolo (AbM), a movement of “over 180,000 shack dwellers” founded in 2005 to advocate for land, housing, and dignity for those living in poverty. On February 12, Mkhize was shot and killed in the eNkanini settlement in Allandale, Gauteng province. He had previously received death threats, including a ransom and a warning to stop his activism against the illegal sale of local land or be killed.

AbM said this was the fifth murder in eNkanini in one year, but “there have been no arrests and the local police have shown no interest in the killings.” The organization has reported threats since 2009 and said after Mkhize’s death, 26 of its members have been killed as a result of activism. However, to date there have only been two related convictions.