By Emma Farge

LAUSANNE, Switzerland (Reuters) -Six Swiss policemen appeared in court on Monday charged over the death of a Black man who suffered a fatal heart attack after he was pinned down during an arrest, a case that one lawyer compared with the death of George Floyd in the United States.

The officers, who are all white, are accused of "homicide through negligence" over the death of Mike Ben Peter, a 39-year-old Nigerian man, in Lausanne in 2018.

They all deny any wrongdoing and say his death was caused by other factors. Their lawyers have dismissed any comparison with Floyd, who died after an officer knelt on his neck for more than nine minutes during an arrest in Minneapolis in 2020.

Ben Peter's death has triggered protests by activists who have accused the Swiss police of institutional racism - charges the force has denied.

The judge opened the trial by saying that it was a "painful case" and asking people watching the proceedings, including Ben Peter's widow and brother, to stay calm.

Simon Ntah, the lawyer for Ben Peter's family, told the court that it was an "insult to intelligence" to consider the death an accident.

He said the position in which Ben Peter was held was comparable with the one endured by George Floyd, and had "ultimately provoked a heart attack".

Ntah said Ben Peter was one of four Black men who had died during police interventions in Vaud canton since 2016. He showed the court a photo of an officer, his face pixelated, giving a thumbs-up sign next to 'RIP MIKE' graffiti.

Defence lawyer Juliette Perrin dismissed the comparison with Floyd's case. "It's not at all the same thing," she said. Two defence lawyers questioned the reliability of witnesses who described the arrest, saying one was short-sighted and saw the event from a high balcony. "These are not reliable witnesses," lawyer Odile Pelet said.

According to the indictment, the officers first noticed Ben Peter during a drug patrol after he collected a bag later shown to contain marijuana.

The indictment said Ben Peter did not comply with police requests and the officers used pepper spray and knee kicks to the ribs and crotch to get him on the ground and handcuff him.

It said he continued to struggle as he was held face-down by several officers for three minutes, until they noticed he appeared unconscious.

Ben Peter was later pronounced dead after a heart attack with multiple causes, the indictment said, including the fact that he was held on his stomach and subjected to stress but also his obesity.

The officers each face a maximum sentence of three years in prison if convicted. Swiss privacy laws mean they can not be named at this stage in the proceedings.

A group of U.N. experts said last year there was systemic racism in Switzerland in a report that raised serious concerns about "excessive use of force and the expectation of impunity by police" and cited this case.

A government-mandated study acknowledged the problem was structural and said measures had so far been insufficient.

(Reporting by Emma Farge in Lausanne, SwitzerlandEditing by Matthew Lewis and Andrew Heavens)