UN rights experts voiced deep concern Thursday at the slow pace of an investigation into the killing of Lebanese intellectual Lokman Slim two years ago, demanding that Beirut ensure accountability.

“It is incumbent on the Lebanese authorities to fully investigate and bring to justice the perpetrators of this heinous crime,” the four independent experts said.

“Failing to carry out a prompt and effective investigation may in itself constitute a violation of the right to life.”

A secular activist from a Shia family, 58-year-old Slim was found dead in his car on February 4, 2021, a day after his family reported him missing.

His bullet-riddled body was found in southern Lebanon -- a stronghold of the Iran-backed Hezbollah movement of which he was heavily critical.

In their statement, the UN special rapporteurs on extrajudicial executions, the independence of judges and lawyers, the right to freedom of opinion and expression and the situation of human rights defenders voiced outrage that no one responsible for his assassination had been identified.

“Shedding light on the circumstances surrounding the death of Mr. Lokman Slim and bringing those responsible to justice is also part of the State’s obligation to protect freedom of opinion and expression,” said the experts, who are appointed by the UN Human Rights Council but who do not speak on behalf of the world body.

“A culture of impunity not only emboldens the killers of Mr. Slim, it will also have a chilling effect on civil society as it sends a chilling message to other activists to self-censor,” they said.

The experts stressed that investigations into unlawful killings must be “independent, impartial, prompt, thorough, effective, credible and transparent.”

“Thus far, national authorities have shown no indication that the ongoing investigations are in line with relevant international standards,” they warned, demanding that the authorities speed up the probe and “ensure that those responsible are held accountable without delay.”

“Mr. Slim’s family must have access to justice, truth and adequate reparation expeditiously.”