Just after a takeoff, a male passenger on Flight MH128 tried to enter the cockpit while holding what one passenger described as a "huge, unusual, black, metallic, strange thing... size of a watermelon."
"He was yelling 'I need to see the pilot, I need to see the pilot,'" passenger and former AFL player Andrew Leoncelli told Australia's ABC News.
The mid-flight scare ended safely, but passengers later criticized the police response which saw them sit on the tarmac for 90 minutes with what they thought could be a bomb on board, according to the Australian Broadcasting Corporation
"We could see them [the police] all outside, but they weren't coming on the plane and nobody knew why," passenger Selena Brown told the ABC.
Man 'recently released from psychiatric care'
During a press briefing Thursday, Chief Commissioner of Victoria Police Graham Ashton said police initially treated the incident as terror related.
"Counter-terrorism response and protocols kicked in... for us that meant having the plane isolated, and as soon as practicable, getting the passengers off the plane safely and dealing with the offender," Ashton said.
Ashton confirmed the passenger approached the flight deck with something many feared could be a bomb.
"He was certainly at the cockpit door, seeking entry to the door, holding this device," he said. "The device was described as an amplifier type instrument... it can potentially be wired up and dealt with in a dangerous manner."
After flight staff intercepted the man at the cockpit, he was chased down the aisle by other passengers to the back of the plane, where they used a spare seat belt and cables to tie him up.
"He was essentially trussed up as the flight returned to Melbourne," Ashton said.
Police later identified the suspect as a 25-year-old Sri Lankan man who had recently been released from psychiatric care. He was not considered a terror threat, they said.
Malaysia Airlines confirmed the flight was forced to turn back to Melbourne due to a "disruptive passenger."
"An investigation led by Australian authorities is currently underway and Malaysia Airlines wishes to extend its appreciation to everyone involved during the emergency situation," it said in a statement.