Johnny Go had fallen at the first fence and ran loose before coming down on the run-in.
He was being treated while the race was being run and suffered a fatal injury.
‘Stop-race’ procedures were put into place by the racecourse executive while Johnny Go was being attended to behind screens near the finishing line, with the race subsequently declared void.
But Quinlan, rider of first-past-the-post Red Giant, Derek Fox aboard Miss Joeking - the only other finisher - and Stephen Mulqueen, who was unseated from Here Comes Love after the final fence, appeared to ignore the ‘stop-race’ flag waved to raise attention to the stricken horse and were hit with hefty suspensions.
A stewards’ report read: “An inquiry was held to establish the reasons why the riders in this race failed to pull up after the yellow ‘stop-race’ flag had been deployed.
“They interviewed riders Sean Quinlan, Derek Fox and Stephen Mulqueen, the clerk of the course and the assistant head groundsman.
“Having heard their evidence and viewed recordings of the incident, and in light of the ‘stop-race’ flag being deployed in the home straight, under rule (B)66 the stewards declared the race void.
“They found Quinlan, Fox and Mulqueen in breach of Rule (B) 48.1.1 and suspended each of them for 10 days.”
Robin Mounsey, head of media for the British Horseracing Authority, added: “The rules of racing are clear that once the ‘stop-race’ flag is deployed, the jockeys must stop riding and the race is void.
“The ‘stop-race’ flag is used for safety reasons and jockeys are aware that they must stop riding immediately once they have seen the flag being waved, and that the stewards have no choice but to declare the race void.
“The decision to deploy the ‘stop-race’ flag, and where to deploy the flag operator, is made by the clerk of the course.
“If any riders continue racing after they have seen the flag, the stewards will then hold an inquiry to determine whether any rules have been breached, and will consider evidence from the jockeys and clerk of the course.”