Kenyan President William Ruto on Wednesday condemned the death of a man in police custody that has sparked widespread anger as the country prepares to mark a year since massive protests calling for change.

Albert Ojwang, 31, was arrested in western Kenya over posts on social media accusing police deputy inspector-general Eliud Kipkoech Lagat of corruption.

He was transferred to the central police station in the capital Nairobi where he died over the weekend, with police initially saying he had hit his own head against the wall of his cell.

But a government pathologist said Tuesday the injuries were “unlikely to be self-inflicted”.

The case has sparked anger online and small protests at a tense moment for Kenya, which is marking a year since protests over tax rises and corruption that triggered a police response in which at least 60 people were killed.

“This tragic occurrence, at the hands of police, is heartbreaking and unacceptable,” Ruto said.

The president urged officers to cooperate fully to facilitate a “swift, transparent and credible investigation”.

Police chief Douglas Kanja addressed the Senate to say that Ojwang was arrested for sharing a fake newspaper front page, accusing the deputy inspector-general of corruption and calling him “The Mafia Cop”.

Interior Secretary Kipchumba Murkomen said the government was “committed to ensuring that everyone who was involved in the crime is brought to justice”.

Police have removed five officers from active duty while the investigation is ongoing.

Rights groups also say dozens of people have been illegally detained for taking part in last year’s protests, with many still missing, and others have been arrested for mild criticism of Ruto and the government.