The woman, who had been with Campbell on a separate board, desperately tried to reach Campbell after he fell in the water but was forced to return to the shore to call for help, according to the Daily Mail.
Sources told the outlet that it was a Secret Service agent who then called emergency services from the Edgartown estate to report the incident.
The witness spoke with investigators on shore and was lucid and clear, and showed no signs of intoxication, insiders told the outlet.
More than a week after the July 23 incident, authorities have only released small details of the incident, withholding the names of nearly everyone involved.
The call came in at 7:46 pm, with emergency services responding to a report that the 45-year-old Obama employee had fallen off his board into the water, briefly struggled to stay afloat, and then went under.
A multi-agency search continued into the night with divers, boats, and ground searches underway by multiple state and local agencies.
The witness directed first responders to the area where Campbell was said to have gone under, but no body was found at that location. Authorities also searched nearby properties in hopes that he made it to shore.
On Monday morning, Campbell was located by Massachusetts Environmental Police who deployed side-scan sonar, located around 100 feet from shore in 8 feet of water.
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