An inquiry into the start of the Crabbie's Grand National was referred on to the British Horseracing Authority after jockeys chose not to participate in the on-course hearing.
Officials called an inquiry after the starter reported the riders had lined up despite being advised by the assistant starter, who was positioned in front of the field, that it was not yet race time and then proceeded towards the start.
The stewards report said that when the riders moved forward towards the start they knocked down the assistant starter, thereby comprising the welfare of an official.
After taking initial evidence from the riders and the starting team, the stewards adjourned the inquiry to consider the matter.
The report said that in attempting to reconvene the inquiry after the last race, the riders, who had not been given permission to leave the course, refused to attend the inquiry.
The only rider not involved was Brendan Powell, whose mount, the Johnny Farrelly-trained Battle Group, planted himself at the start and refused to race.