Federal investigators were closing in on Greg Lindberg. FBI agents confronted the North Carolina insurance tycoon last year as they probed whether he tried to bribe a state regulator. In March, officials obtained a sealed warrant for his arrest. His attorneys were negotiating his surrender.

Mr. Lindberg also had something else on his mind—the comings and goings of a number of women he was dating, interested in dating or, in at least one case, cultivating as an egg donor for his future offspring.

Mr. Lindberg paid for dozens of surveillance operatives to tail the women up to 24 hours a day, taking surreptitious photos and sometimes putting GPS trackers on their vehicles, according to former security staffers and copies of internal reports produced by these operatives that were reviewed by The Wall Street Journal.

“Information of Concern: Romantic Encounter,” read one such report just days after the arrest warrant was issued. Lindberg operatives had followed a Los Angeles woman as she met a man at a bar, then to his house, where she left “in the early morning hours.”

One Lindberg agent spied on a different woman by secretly enrolling in a school she attended, while his staff kept tabs on yet another by renting an apartment across the hall from hers, according to the reports and former staffers.