The Boeing 777-200's cargo of mangosteens has also come under scrutiny besides the food served on board the Beijing-bound airliner that disappeared from radar screens on March 8, one hour after taking off.
Khalid said the police had to scrutinise carefully to rule out sabotage.
“We must be very thorough and we need all the time ... you cannot hurry us,” he said.
The police is treating the case as a criminal probe.
Malaysian Prime Minister Najib Razak will be in Perth on a two-day tour to oversee the search for the plane.
Malaysia has come under criticism from aviation experts and families of the 239 victims of the plane crash over handling the probe.
On the 25th day of the multinational search operations, a British nuclear submarine joined the hunt for the plane in the Indian Ocean.
According to media reports here, Britain's Royal Navy submarine HMS Tireless arrived in the search area about 1,500 kilometres northwest of Perth this morning.
The personal jet of Peter Jackson - Oscar-winning New Zealand movie director - is also being used in the hunt.
Up to 10 planes and nine ships participated in today's search for the Boeing 777-200, the Joint Agency Co-ordination Centre (JACC) in Perth managing the operations said in a statement.
The Australian Maritime Safety Authority has determined a search area of about 221,000 square kilometres, 1,504 kilometres northwest of Perth.
Retired Australian Air Chief Marshal Angus Houston, heading the JACC, yesterday said it was the most challenging search and rescue operation he had ever seen and said efforts to trace the wreckage could take time.
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