The NIA on Tuesday said it had taken over the case wherein Jet Airways Mumbai-Delhi flight was diverted to Ahmedabad on October 30 following a security threat.

A National Investigation Agency (NIA) official said the case was taken over by the agency as Gujarat Police registered the case under the anti-hijacking law and arrested Birju Kishore Salla, a Mumbai-based diamond businessman.

The flight 9W-339, with 122 passengers, including seven crew, made an emergency landing at the Ahmedabad airport after a letter warning about a hijack and bomb threat was discovered in the plane’s toilet.

The pilot had alerted the Ahmedabad airport authorities about the threat letter, reported to be in Urdu and English.

The plane was taken to a remote bay at Ahmedabad airport and all passengers disembarked and screened. It was later cleared for take-off.