> You can't arrest somebody for a sabotage without letting him to execute the deed.
Sure you can. We convict people of conspiracy all the time.
https://www.law.cornell.edu/wex/overt_act
Arresting all the people who happen to walk past a strategic object will fill up your prisons very quickly.
Arresting all the people who happen to walk past a strategic object will fill up your prisons very quickly.