When David J. Garrow, a Pulitzer Prize-winning biographer of the Rev. Dr. Martin Luther King Jr., sat down last spring to dig through a trove of previously unreleased government records, it was business as usual for a researcher known for prodigious reporting and doorstop books.

“There’s this weird ability I have of complete recall with regard to what I already know and don’t know,” Mr. Garrow said, describing the experience of wrestling with some 54,000 separate web links posted by the National Archives and Records Administration. “I was just scrolling through the PDFs, looking for new little factoids.”

Mr. Garrow found factoids aplenty, about the Federal Bureau of Investigation’s infamous surveillance of Dr. King — and, most controversially, about alleged sexual misconduct by the civil rights leader.

In a 7,800-word article published last week by the British monthly magazine Standpoint, which teased the piece on its cover as “Martin Luther King and #MeToo,” Mr. Garrow provides new details about the F.B.I.’s tactics alongside graphic descriptions from documents recounting alleged group sex in bugged hotel rooms. He also names some of Dr. King’s purported lovers, including fellow activists who have never been publicly identified as such.