The newspaper said Friday it's asking a third party to conduct the probe but didn't detail what prompted it.
The Globe was awarded a 2014 Pulitzer Prize for its coverage of the Boston Marathon bombings the year before. Cullen was a finalist for commentary.
Boston sports radio station WEEI has pointed to what it describes as inconsistencies in Cullen's coverage. It notes a column in which Cullen wrote about how horrifying it was "to watch as first responders frantically pulled metal barriers" to get to the injured. It says Cullen in a subsequent interview said he was 1 mile (1.6 kilometers) from the finish line when the bombs went off.
Cullen hasn't responded to a Twitter message seeking comment.
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