Racing at Newbury in England was abandoned on Saturday after two horses collapsed and died in the parade ring.
Fenix Two and Marching Song were being paraded before the first race when they fell to the ground.
The joint managing director of the course, Stephen Higgins, told the BBC an electric cable has been found under the paddock.
He says the cable is being excavated to identify whether it has been damaged, how deep it is and the true cause of the tragedy.
Seven horses made it to the start but the remainder of the day's racing was abandoned as a precaution.
There has been racing at Newbury for 104 years.