From October 2015 to July 2018, an FBI double agent conducted "dead drops," in which, authorities say, Peng fetched information in the San Francisco Bay Area and Columbus, Georgia.
Sounds like the FBI may have used him as a conduit to feed China false information. If so, that might be the reason for the 3-4 year delay in arresting him, feeding false info, letting the false info percolate into Chinese decision-making, projects, and plans.