Francesco Tedesco says Stefano Cucchi was kicked and punched in the face by officers

An Italian police officer has told a court he witnessed the beating of a 31-year-old man who died after being held in police custody in 2009, in a major development in a case that has gripped the country.

Francesco Tedesco, one of three military police officers charged with the murder of Stefano Cucchi, told a courtroom in Rome his colleagues had kicked and punched Cucchi in the face, causing his death. Tedesco also alleged he had been threatened by officials who told him to keep quiet and conceal his report about the incident.

“I say sorry to the Cucchi family,” Tedesco told the court. “The last few years have been an insurmountable wall for me. It was not easy to report [on] my colleagues.”

Cucchi was arrested on 15 October 2009 in a park in Rome. He was found in possession of about 20g of hashish and three packets of cocaine.

A week later, he was found dead in a room at Sandro Pertini hospital in Rome, where he had been taken for treatment for injuries including two fractured vertebrae and a broken jaw. He weighed 37kg at the time of his death, and photos of his gaunt appearance and bruised eyes shocked Italians.

In October 2014, a judge acquitted the officers due to a lack of evidence. A wall of silence from authorities meant it was impossible to determine who was responsible for his death.

Cucchi’s sister, Ilaria, said after the verdict: “My brother is just another person killed by the silence. Nobody cared about him.” She has fought a long and lonely battle to find out the truth about what happened.

In December 2015, the supreme court of cassation in Rome reopened the case and a new trial began.

As the case dragged on, Italy’s far-right interior minister, Matteo Salvini, then an MP, sided with the police. “It is difficult to imagine the police and carabinieri beat up Cucchi for the sake of it,” he said in 2016. “I am always on the side of the police and carabinieri.”

The turning point came in October last year, when Tedesco began to collaborate with prosecutors, confessing the details of the killing.

Facebook Twitter Pinterest A scene from the Alessio Cremonini film On My Skin, which was inspired by the case of Stefano Cucchi. Photograph: Angelo Turetta/Netflix

Tedesco revealed the existence of a service note written by him in which he related the alleged abuses perpetrated against Cucchi. Tedesco said the service note was made to disappear on the orders of military police officers, who are now under investigation over a cover-up.

“I was alone, backed into a corner,” Tedesco told the court this week. “I panicked when I realised my service notes had vanished.” He said a superior had told him “you have to follow the thin blue line if you want to continue to be a carabiniere”, adding: “I sensed a threat in his words.”

The case inspired On My Skin, a film by Alessio Cremonini that won three David di Donatello awards, the Italian equivalent of the Oscars.

Ilaria Cucchi said this week that after 10 years of lies and cover-ups, truth had come to the courtroom. “Today, we finally feel less alone,” she added.