Terrorists usually don't claim responsibility for their actions until the fuse is lit, it's not a case of Jack The Ripper sending an ear to the cops and warning them who his next victim will be. Terrorists usually do claim responsibility for their actions after the media is aware that something happened, this gains recognition for their cause, which is often the reason they resort to terrorism in the first place. These groups are often underground and individuals rarely step forward, how can you arrest an entire group that you can't touch?
Governments endorsing terrorist acts and providing a safe house for them once they're on the run just adds to the problem. Hijackers can take their hostages, get the ransom and fly the plane to the country of their choice. That country is usually ready to welcome the criminal, for a small cut of the ransom. Algeria used terrorism as a business to raise capital. By providing immunity, they became a haven for terrorists.
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