If somebody kept using the same phone line to trigger bombs, do you think that the phone company doesn't have an obligation to shut that line down? Let's say the police came to the phone company and said "we know that if you shut this phone line down, so and so wont be able to trigger the bomb they have planted in XYZ space." Do you think the phone company should do nothing?

What about a courier that knows it is delivering bombs? We should look past that too?

Which principles are you invoking exactly?