A full investigation should reveal how the gun was smuggled in
to prevent it from happening again.
Security/Catering/Cabin Crew/Cleaners/Engineering all to be interrogated to determine actual culprits ... that's the way forward and logical.
In India's case, within minutes, they already have the knowledge that 300Kgs of explosive laden vehicle was used in the attack, attacker was though local but trained in Pakistan and Jaish-e-blah blah blah accepted the responsibility by sending BT to Modi.