The horses collapsed in front of stunned onlookers in scenes unprecedented in the sport.
Newbury's joint managing director, Stephen Higgins, said it was a "distinct possibility" that an old electric underground cable had been disturbed, and on Sunday a piece of cable was taken away.
Stuart Hogarth, operations director for Southern Electric Power Distribution, said: "A section of electricity cable has been removed from the paddock area for further detailed inspection.
"Our initial on-site investigations last night confirm there was no danger to the public."
Mr Higgins said they had received reassurance that the site is safe.
"We hope that the final results of this investigation will be established as soon as possible," he said.
Altogether, four horses were affected. Fenix Two and Marching Song died, Kid Cassidy was withdrawn at the start, and the Merry Giant ran but tailed off badly.
The two that died had steel shoes while the other two were wearing aluminium plates.
Racing was called off for the day after the first event but talks are continuing to see whether some or all of the six abandoned races can be re-staged.
The much-anticipated meeting was among the last major ones before the Cheltenham Festival in March.
"We are in conversation with the Tote who were sponsoring the vast majority of the card and they've got an appetite, to some degree, to see racing re-staged later in the week," Mr Higgins said.
Former champion trainer Nicky Henderson, who withdrew Kid Cassidy at the start after the horse had buckled in the paddock, told BBC Radio 5: "I think it was one of the most traumatic five minutes one could ever go through."
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