[5] In 1965, Douglas abandoned his studies after earning poor marks, and in 1966 began a four-year enlistment in the United States Air Force.

[10][11][12] While traveling around the country providing instruction to police, Douglas began interviewing serial killers and other violent sex offenders at various prisons.

He interviewed some of the most notable violent criminals in recent history as part of the study, including David Berkowitz, Ted Bundy, John Wayne Gacy, Charles Manson, Lynette Fromme, Sara Jane Moore, Edmund Kemper, James Earl Ray, Sirhan Sirhan, Richard Speck, Donald Harvey and Joseph Paul Franklin.

[15] Douglas first made a public name for himself with his involvement in the Atlanta murders of 1979–81, through an interview he did with People about his profiling of the as yet unidentified killer as a young Black man.

Douglas thought the killer would be an experienced hunter with low self-esteem, have a history of being rejected by women, and would feel compelled to keep "souvenirs" of his murders, such as a victim's jewelry.

Douglas provided information after four members of the Chaney/Culbert family were murdered in July 1985, comparing similarities discovered at the crime scene to evidence found at the homicide of Debra Ford a year earlier.

[22] In January 2015, creators of the television show Criminal Minds confirmed that the characters of FBI profilers Jason Gideon and David Rossi were based on Douglas.

[25] Prior to the Netflix series, a TV documentary version of Mindhunter had run on MSNBC, in which Douglas interviewed other notorious serial killers such as Joseph Kondro and Donald Harvey.

[26] Many of Douglas' interviews in connection with Mindhunter subsequently featured in his books, including in The Killer Across the Table, in which Douglas provided detailed depictions of psychopathy particularly in the cases of Kondro and Joseph McGowan, who had targeted preteen girls whom they personally knew and were daughters of friends or neighbors, and of Harvey, one of the country's most prolific serial killers who used his position as a hospital orderly to commit dozens of murders of patients.