Drafted in 1972, he served three years in Vietnam. After his return, he earned a Master's degree in counselor education and applied to the FBI, but a hiring freeze led to his taking a job as a psychologist with the N.C. Department of Correction. Brantley worked first at Dorothea Dix psychiatric hospital, then later worked across the street at Central Prison in Raleigh. Part of his job was conducting analyses for prerelease or parole hearings, dealing with inmates with mental problems, and “putting out fires” by heading off potentially dangerous situations.
After six years there, Brantley saw a television ad in which the FBI was looking for new agents, and he joined just as the FBI was launching its Behavioral Science Unit. He said he was a beneficiary of good time, because the FBI was starting to hire people with diverse backgrounds. He went through about three months of training in Quantico with the goal of being a profiler.
He served with the National Center for the Analysis of Violent Crime, which was originally focused mostly on serial killers, but also on any criminal committing serial assaults, or on any case where there was evidence or belief that the perpetrator might repeat the crime. He worked on the case of Angel Maturino Resendez, known as “The Railroad Killer,” who in some ways was the antithesis of the cunning madman and broke the conventional-wisdom serial killer mold that said such killers stick to their own ethnic groups, and was finally caught in 1999.
Brantley helped with the investigation into the Oklahoma City bombing of a federal building in 1995 and, after violent standoffs with David Koresh’s Branch Davidians and the Weaver Family at Ruby Ridge had brought criticism of federal actions, Attorney General Janet Reno formed a group of experts as a “Critical Incident Response Group” as part of Brantley’s unit. Later standoffs with a Freemen group in Utah, a Republic of Texas group, and a group in Boston were resolved without catastrophic loss of life.
One of Brantley’s last major cases was the D.C. sniper hunt, when two men were arrested after a shooting spree that killed 13 over a three-week period.
As a researcher, Brantley had the opportunity to interview a significant number of killers.
Brantley and another former FBI agent formed MAG International when they retired to serve as a consulting firm. As a consultant, Brantley reviews and sometimes testifies in cases.