The people spoke to the AP on condition of anonymity because details of the investigation won't be made public until former FBI director Robert S. Mueller III releases his report. The report is expected to be completed this month, one of the sources said.
Mueller has been investigating whether anyone at the NFL had seen or obtained video of the former Baltimore Ravens running back striking his then-fiancee inside an elevator at an Atlantic City, New Jersey casino before the video was published online.
League employees were instructed to co-operate with Mueller's team of investigators and respond immediately to requests for information, the sources said.
Investigators zeroed in on phone calls made from NFL offices to numbers with a New Jersey area code. Employees also were asked to identify certain numbers in question and investigators even called some of the numbers to verify call recipients.
A representative for Mueller, who led the FBI for 12 years under Presidents George W. Bush and Barack Obama, declined comment.
Mueller's team is trying to identify who called a law enforcement official who said he mailed a DVD of the video to league headquarters to the attention of the NFL's security chief. The official played for the AP a 12-second voicemail from an NFL office number dated April 9, where a woman confirms receipt of the video.
Mueller now works in private practice in a Washington law firm. His probe is being overseen by owners John Mara of the New York Giants and Art Rooney of the Pittsburgh Steelers and the league said three months ago that Mueller would have access to all NFL records and would have full co-operation from league personnel.
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