Director of Public Prosecutions Noordin Haji has ordered Inspector General of Police Joseph Boinnet to investigate the Wednesday crash that killed 56 people.
Haji wants Boinnet to find those accountable for the Fort Tenan, Kericho road accident that left 16 with serious injuries.
"In exercise of the powers conferred upon me under Article 157(4) of the Constitution of Kenya, I hereby direct that you cause investigation into the matter to determine the persons who may have, through acts of commission or omission, directly or indirectly contributed to the occurrence of the accident," he told Boinnet in a letter.
He added: "The investigation should be extended to cover all agencies of government charged with the responsibility of ensuring safety on our roads as well as the owners of the subject motor vehicle."
The killer bus christened 'Home Boyz' was headed to Kakamega with 71 passengers, 9 more than the legal capacity.
National Transport and Safety Authority (NTSA) on Thursday said the Western Cross Express bus (KBS 029J) was not licensed to operate at night.
This is as two suspects who have been arrested in connection with the accident are due in court later today.
Owner of the bus Bernard Ishundu and the director of Western Cross Express Company Ltd, Cleophas Shimanyula will know their fate if they will remain in police custody as investigations continue.
Detectives had asked Chief Magistrate Samuel Wahome that they be detained for seven days at Londiani Police Station pending rulling.
Ishundu and Shimanyula are accused of not keeping the records of the driver and conductor who operated the bus at the time of the accident, contrary to the Traffic Act.