Malaysia’s top police officer, Khalid Abu Bakar, admits a three-week investigation has been inconclusive and that investigators may never discover what caused the plane’s disappearance.

“Give us more time,” Inspector-General Khalid told Bernama, Malaysia’s state news agency.

“We may not even known the real cause of this incident,” he said.

As the relatives of passengers angrily accuse Malaysian authorities of withholding information, Inspector-General Khalid said releasing some details could jeopardise the largest and most complex investigation undertaken in Malaysia.

“I’m sorry, there are things we cannot reveal to you … not that I don’t want to reveal to you, but we cannot do that because it’s a criminal investigation, ongoing,” he said.

“We have not concluded the whole thing and we are still awaiting reports from experts overseas and internally.”

Inspector-General Khalid said: “Who knows, maybe there will be prosecution later on. So this will affect the prosecution’s case, if we start revealing our findings.”

The police investigation has focused on the possibilities of hijacking, sabotage or psychological problems among passengers or crew.

FBI forensic experts are still examining a flight simulator that was seized from the home of senior pilot Zaharie Ahmad Shah, 53, but have so far not found anything suspicious.

Police have so far interviewed 170 people.

Lack of information about the investigation has fueled unsubstantiated conspiracy theories in Malaysia’s social media.

One of the most popular is that the plane was diverted by CIA operatives masquerading as passengers to the US military installation in Diego Garcia in the Indian Ocean.

According to the theory, cargo in the plane was related to the technology of unmanned drone flights.