LONDON, Nov 1 (Reuters) - London's police force was found guilty on Thursday of putting the public at risk over the killing of an innocent Brazilian, gunned down after being mistaken for a suicide bomber in 2005, the BBC reported. Police shot electrician Jean Charles de Menezes, 27, seven times in the head after he boarded an underground train in south London on July 22, 2005. They had wrongly identified him as one of four men who tried to attack the city's transport system a day earlier. The Office of the Commissioner of the Metropolitan Police faces a large fine now that it has been found guilty of the single charge of breaching health and safety rules which require it to protect the public. Prosecutors had accused the force of a "shocking and catastrophic error" during the trial at the Old Bailey, in what was seen as an extraordinary use of workplace health and safety laws against a police force.