Three former G4S guards were cleared yesterday of manslaughter over the killing of an Angolan man on a deportation flight from Heathrow, prompting campaigners to demand more accountability for private security firms. The three men had been accused of using a restraint technique known as “carpet karaoke”, and held down 46-year-old Jimmy Mubenga for more than half an hour while ignoring his increasingly desperate warnings that he could not breathe…But the restraint of pushing a seated person’s head forward, compressing the diaphragm to stop them spitting, was later deemed “malpractice”…The men said they had only restrained Mr Mubenga to stop him from hurting himself or others and said they had never heard him shouting that he was struggling to breathe...Deborah Coles, of the rights group Inquest, said: “There needs to be a mechanism for state institutions and the private companies they employ to be held to account when people die"…