https://www.newyorker.com/news/news-desk/prisoner-swap-obamas-secret-second-channel-to-iran

What heightened the risk was the fact that the new Iranian team was headed by a senior intelligence official, a sharp departure from the traditional but still tentative diplomatic channels with the Iranian Foreign Ministry developed in the nuclear talks. The involvement of Iranian intelligence made prospects far more unpredictable—and potentially controversial. Brett McGurk, a senior State Department official, headed the small American team, which also included officials from the Department of Justice, the F.B.I., and the intelligence community.