Dubai ruler Sheikh Mohammed's Godolphin will face no further charges over horse doping at its Moulton Paddocks stable in England, it was announced on Thursday.
The British Horseracing Authority said it has concluded its investigation into one of the most serious doping scandal in recent British racing history.
The BHA said there was no evidence of any other parties, beyond those identified at a hearing on April 25, being involved in the distribution of anabolic steroids, other than former trainer Mahmood Al Zarooni, who was suspended for eight years.
The ban was imposed on Al Zarooni after 22 horses, including last season's St Leger winner Encke, tested positive earlier this year.
The investigation also found a number of key failings both in terms of process and within the management structure at the yard which enabled Al Zarooni to carry out the offences without being detected, the BHA said on its official website.
Al Zarooni's assistant, Charlie Appleby, assumes control of Moulton Paddocks with immediate effect, it added.
The BHA said it was happy Appleby had no knowledge of Al Zarooni's wrongdoings and that he has already begun implementing some procedural changes alongside fellow Godolphin trainer Saeed bin Suroor.
Adam Brickell, director of integrity, legal and risk for the BHA, said in a statement: "After an extensive and thorough investigation we have found no new evidence which contradicts that which was presented to the disciplinary panel.
"The evidence gathered from this investigation has confirmed that Mahmood Al Zarooni acted autonomously and was the person solely responsible for the events that took place at Moulton Paddocks.
"However, we have identified significant failings in the processes in place and management structure at the yard which allowed these events to unfold without senior management becoming aware. These findings have been shared with Godolphin."
Paul Bittar, chief executive of the BHA, added: "The investigation process has been a complex and challenging one. However, I am satisfied that the conclusions reached are an accurate reflection of events. Fortunately cases such as this - both in terms of scale and profile - are incredibly rare, however there are areas where we can learn from the issues raised."