Reporting and Airline Security

Curious what you think of this case. A reporter in New Zealand followed up on a story on an in-flight stabbing aboard an airplane by boarding a flight with a knife and a fake gun in carry-on luggage.
What are the ethical implications here? How do you weigh the risk the move posed against the public benefit of pointing out holes in the security system? Should the reporter be prosecuted? Or was this exactly what journalism is supposed to do?