Finnegan Lee Elder and fellow US student Gabriel Natale-Hjorth stand accused of killing Mario Cerciello Rega, who was in plain clothes when he was slain in a night drug bust on July 26th last year in an attack that sparked national outrage.

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“They beat me pretty bad … in the [police] station,” Elder was secretly recorded as saying during a private conversation in prison with his father and American lawyer.

“They threw me to the ground, kicked me, punched me, stood on me, spit on me,” he said according to a transcript of the conversation requested by the court and seen by AFP late on Wednesday.

The two Americans, who were teens at the time, face life sentences if found guilty of knowingly killing a police officer.

The claim of police brutality follows the leaking of photographs of Hjorth blindfolded and handcuffed at the Rome barracks where he and Elder had been taken for questioning.

“The awful truth of what Finnegan was subjected to and endured as a terrified 19-year-old is now being revealed to the world,” Elder's father Ethan told AFP. “Our hearts break every minute of every hour of every day.”

Ethan Elder, father of one of the two American suspects. Photo: Filippo Monteforte/AFP

Asked during the conversation at the Regina Coeli prison on August 2nd last year where the police station was, Elder said: “I have no idea – they kept my head down a long time”.

Had he been blindfolded like Hjorth? “No, no, I – I don't really remember too well. … I was, they had me waiting so long, it's kind of a blur,” he said. He said he had got two bruises on his right arm and one on his leg “in the police station”.

“They said they would give me 40 years if I didn't give them my phone password,” he said.

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Elder, 20, has admitted to stabbing Cerciello with an 8-inch combat knife. But he insists Cerciello and his partner Andrea Varriale attacked them and he thought he was fighting for his life against drug dealers.

Varriale says when he and Cerciello stopped the youngsters, they were set upon. Cerciello was left with multiple wounds.

Tributes to murdered officer Mario Rega Cerciello outside a police station in Rome last July. Photo: Vincenzo Pinto/AFP

Natale-Hjorth initially told investigators he had not been involved, but his fingerprints were found on a ceiling panel in the hotel room where the students had hidden the knife.

Under Italian law, anyone who participates even indirectly in a murder can face homicide charges.

The defence says lies told by Varriale in the immediate aftermath of the stabbing — such as whether or not the policemen were armed, as they should have been while on duty — seriously undermine his credibility as a witness.

Last month Elder's lawyers said they had discovered a statement taken during the police investigation, which revealed a key figure in the case was a police informant, had been illegally withheld by the prosecution.