Original Message

While patrol does fall under Part 91, as it is specifically called out in Part 119 as an exception to the Part 135 rules, like most FAA topics- there are exceptions to the rule. 

I'd suggest the OP check out the FAA Office of Chief Counsel opinion website. There is something called "Dual Purpose," whereby the patrol flight can take on a dual purpose and become Part 135. See the Bonilla opinion.