BORDEAUX: French police on Monday launched a delicate operation to lift a helicopter from a river bed for clues into a crash that is thought to have killed a Chinese tycoon and a French winemaker.

Efforts to find the remains of Lam Kok, a 46-year-old Chinese tea-and-property magnate, his interpreter and financial adviser, Peng Wang, and James Gregoire, a French entrepreneur and the pilot of the helicopter, have been ongoing since Friday, when the aircraft fell into the Dordogne River.

The crash occurred while they had been on a celebratory aerial tour of a chateau estate that the Chinese businessman had just bought from Gregoire.

“We are putting in ballasts which will be inflated at the same time to lift the wreckage,” Col. Ghislain Rety, the head of the gendarmerie in the Gironde region, where the chateau is located, told AFP.

“It’s a delicate operation, the aim is to preserve the wreckage in its current form for small details that can explain why it crashed,” he said.

Rety said it could be months before the bodies were recovered.

“We can recover them today or in six months but we will find them,” he said.

“A body was found on Saturday in the Dordogne, it was a person who had disappeared in the river in April,” Rety said, adding that April accident had occurred about 30 kilometers from the site of the helicopter crash.

The investigators conducted a sonar search on Sunday night to scan the river for the bodies.

The scans were to resume Monday along with helicopter searches across a 20-kilometer stretch along the river from where the chopper crashed.

The wreckage of the Robinson R44 helicopter, which is used by the police and army in several countries, was located early Saturday in seven meters (23 feet) of water.

Only the body of Lam Kok’s 12-year-old son Shun Yu Kok, has been recovered.

“Every lead is being followed — the weather, the rules, maintenance, the pilot’s qualifications and the characteristics of the flight,” said Philippe Mole of France’s air transport investigation department.

The Chinese tycoon’s wife had been meant to be on the doomed flight, but declined at the last minute, explaining she was afraid of helicopters.

She and her husband head a Hong Kong company, Brilliant, that dealt in upmarket teas, luxury hotels and the construction and management of shopping centers.

On Thursday, they had bought the Chateau de La Riviere and its 65-hectare (160-acre) of vineyards for a reported 30 million euros ($41 million) with the aim of turning it into an elite tea- and wine-tasting retreat and plans to build a hotel nearby.

After a lavish event Friday publicizing their purchase, Gregoire offered to take the couple up quickly in his helicopter to survey their new property.

When the helicopter did not return after 20 minutes, employees at the vineyard contacted emergency services.

Gregoire himself had bought the property in 2003 — a year after the previous owner died in a plane crash.

Wealthy Chinese have developed a taste for fine French wines, and their buying power has been credited with pushing prices for certain vintages to record levels.

In recent years they have increasingly taken to buying French vineyards as well.