Forty mentally ill patients escaped on Sunday from the Mathari Mental Hospital in Kenya's capital, Nairobi, after overpowering guards, police say. Ten of them have been found, while a search is still underway for the remaining 30, police added. Kenya's Standard newspaper reports that the group escaped from the state hospital after complaining that the medicine given to them was ineffective. Mathari is the biggest psychiatric hospital in Kenya. In 2011, rights groups called for an investigation into alleged human rights abuses at the hospital following a CNN documentary "Locked up and Forgotten". 'Doors broken' The CNN crew reported that during a visit to the hospital, they found a dead body locked up in a seclusion cell with a patient. Senior Nairobi police officer Moses Ombati told the BBC the patients had staged a protest on Sunday, before overpowering guards and escaping. Divisional Police chief Samuel Anampiu said the escape seemed to have been well-planned, AFP news agency reports. "They must have strategized. It is not possible that, without proper planning, 75 people can break two doors and more than half of them run away," he is quoted as saying. Mr Anampiu said eight of the escapees had been brought back to the hospital by their families while another two returned voluntarily. Police were still searching for the other 30 patients, he added. "We have all their particulars and including their pictures and that will make it easy for us to identify them," he said. A patient who returned to the facility, Kevin Kemboi, said he escaped after another patient told him that nurses were on strike, AFP reports. "I just followed one of the patients... then made my way home. At home, I realised the environment was different," he said.