Is it E-Trades (or any brokers?) job to prevent a stock market manipulator from trading or is that the SEC's (or someone else's) job to do. i.e. why can't E-Tr

Is it E-Trades (or any brokers?) job to prevent a stock market manipulator from trading or is that the SEC's (or someone else's) job to do. i.e. why can't E-Trade simply refer it to the govt and have them decide. i.e. "We suspect this person is doing something illegal, but its your job to make that determination and to create the legal structure that allows us to not provide them with a service to continue doing that"? of course if it was "we know" vs "we suspect/worry" that might be different, but if they are debating if they should cut off or not, I can't believe it "we know".