It may be within Twitters terms of service to ban people and censor people, and that may be fine for Twitter, but for a sworn officer to use Twitter to censor people - that is an abuse of power.
Of course, the files also show that Twitter personnel acted in bad faith and didn't follow their own ToS.
If you have allegations of illegality, who determined that? Are you saying FBI should just say "Trust us, it's illegal - we don't need a jury or a judge"?
Since when does the FBI just get to accuse people of things and take their rights away?