A privately funded search for missing Malaysia Airlines flight MH370 has drawn to a close.
US-based company Ocean Infinity had been using a deep-sea vessel to conduct a 90-day survey of a vast area of the southern Indian Ocean.
But it found nothing and Malaysia's government says it has no plans to begin any new searches.
The plane disappeared on 8 March 2014 while flying from Kuala Lumpur to Beijing with 239 people on board.
There are still fierce debates over how the flight ended and the families of those on board say they want search efforts to continue.
"People might think: 'Why are these people still harping on about this, it's been four years'. It's important for people to remember that MH370 is not history," Grace Nathan, whose mother was on MH370, told the Guardian.
The plane was carry 153 people from China and 38 Malaysians. Other passengers came from Iran, the US, Canada, Indonesia, Australia, India, France, New Zealand, Ukraine, Russia, Taiwan and the Netherlands. The 12 crew were all Malaysian.
The hunt for the missing plane formed one of the largest surface and underwater searches in aviation history, covering more than 120,000 sq km (46,300 miles) of the Indian Ocean.
Pieces of debris have been found as far away as Madagascar, but not the main body of the plane.
The official search, involving teams from Australia, Malaysia and China, ended in January last year.
Who conducted the private search?
It has been carried out by Ocean Infinity - a US-based company.
It surveyed an area of about 80,000 sq km (30,888 sq miles), using a fleet of up to eight mini-submarines.
The deteriorating weather in the area as winter approaches now makes operating there impossible for the next few months.
The company had agreed to undertake the search unpaid but would have received a reward of up to $70m if it found the wreckage.
The search began after the likely drift patterns of parts of the plane found along the east African coast had been analysed.
How did the flight end?
Investigators have very limited information about the plane's last hours.
Experts still cannot come to a definitive conclusion as to whether MH370 remained under the pilot's command, or crashed out of control into the sea.
Each of these two scenarios suggests different search areas.
The reasons why the pilot took the airliner off its scheduled flight path and down into a remote stretch of ocean are still unknown, as most of the communication equipment on board had been switched off.
Earlier this month, Australian investigators rejected that the plane was deliberately brought down by the pilot.