LAGOS (Reuters) – A group of activists and celebrities, including a co-founder of the Black Lives Matter movement, have signed an open letter to Nigeria’s president demanding that he hold accountable security personnel accused of shooting anti-police brutality protesters.

The letter, published in the New York Times on Thursday to mark International Human Rights Day, comes nearly two months after what witnesses and Amnesty International say was a fatal clash in Lagos between peaceful protesters and military and police. The military and police deny shooting protesters.

The demonstrators had called for an end to police brutality and a much-hated unit called the Special Anti-Robbery Squad (SARS).

Black Lives Matter co-founder Opal Tometi, 36, an American with Nigerian parents, organized the letter after watching the protests descend into violence. Tometi said she has friends and family in Nigeria, but said it was not difficult to get others to sign on.

“We care about the issues of police brutality no matter where they’re occurring,” she told Reuters in an interview on Wednesday. “The violence that people have been met with is intolerable.”

Spokesmen for President Muhammadu Buhari did not immediately respond to a request for comment. Police disbanded SARS on Oct. 11, and the government asked each state to form judicial panels to investigate claims of brutality, but protesters have outlined a campaign of harassment since the shootings, and some still do not know what happened to their missing friends and family.

The letter, signed by supporters including climate change campaigner Greta Thunberg, also asks the government to release jailed protesters, lift a ban on protests and allow an independent human rights monitor investigation into “the actions that led to the killings at Lekki Toll Gate.”

“People are missing and people have died as a consequence of speaking out,” Tometi said. “We will not abide by it.”