The answer is "None. Conducting surveillance of "lone wolves" is legal under the USAPA."
The most concerning issue with lone wolves is likely that the majority of them originate from non-religious foundations and display no indication of devotion. In every practical sense, they can barely be delegated religious fear mongers. The American and European assaults were for the most part directed by individuals who were unmistakable on observation cameras, which prompts over the top security worry on the best way to recognize solitary wolves when they appear to fit in so well with others.