MOSCOW (AFP) ― Russian investigators on Tuesday accused senior airport officials of criminal negligence over a plane crash at a Moscow airport that killed the head of French oil giant Total, Christophe de Margerie, whose private jet hit a snow plough on takeoff.

Several executives would be suspended, the investigators said of the accident which also killed three crew members. They added that the driver of the snow-clearing machine was drunk on the job ― a claim disputed by his lawyer.

At Total, one of the world’s biggest oil companies, staff at its Paris headquarters observed a minute‘s silence for their charismatic 63-year-old boss, who had been known by the affectionate nickname “Big Moustache.”

“The group is set up to ensure the proper continuity of its governance and its activities, to deal with this tragic event,” Total’s secretary general Jean-Jacques Guilbaud said, as top executives were due to hold an emergency meeting.

One of France’s best-known business leaders, De Margerie was an outspoken critic of Western sanctions against Russia over the Ukraine crisis, and just hours before his death had met Russian Prime Minister Dmitry Medvedev at his country residence outside Moscow to discuss investment, local media reported.

Even as relations between the West and Russia deteriorated to the worst since the Cold War, the French oil boss had criticized the sanctions, calling them “a dead-end” and urging “constructive dialogue” instead.

Russian President Vladimir Putin described De Margerie as “a true friend of our country, whom we will remember with the greatest warmth.”

In France, President Francois Hollande said he learned of De Margerie’s death with “shock and sadness,” while Prime Minister Manuel Valls said France had lost “a great captain of industry and a patriot.”

Vnukovo airport said the Falcon Dassault business aviation jet crashed as it prepared to take off for Paris. Visibility was 350 meters at the time, it said, as Moscow saw its first snowfall of the winter on Monday.

Images on Russian television showed the remains of the Falcon-50’s charred cabin on the grass near the runway, its tail and one of the engines close by.

The Interstate Aviation Committee, which investigates all Russian air accidents, said senior airport officials were to blame for causing the accident through “criminal negligence” as they failed to ensure proper staff coordination.

Poor weather, an error by air traffic controllers and the allegedly drunk snow plough driver will also be investigated as possible causes of the crash, it said.

Late Tuesday French experts arrived in Moscow to assist the Russian investigators in the probe, Russian television reported.

Moscow transport investigators said they had opened a criminal probe into breaches of aviation safety rules causing multiple deaths through negligence, which carries a maximum jail term of seven years.

“Why was a vehicle on the runway? Traffic controllers in the tower are expected to ensure that this does not happen, it’s their job,” Victor Gorbachev, general director of the Moscow-based Airport Association, told Russian radio.

The 60-year-old snow plough driver appeared shocked as he was taken into custody for 48 hours, hiding his face from the cameras as he was escorted by emergency services.

“My client has chronic heart disease, he doesn‘t drink at all. His relatives and doctors can confirm this,” his lawyer Alexander Karabanov told the Interfax news agency.

“We don’t want the responsibility for the accident to be shifted to just another ordinary man,” he added.

De Margerie had been chief executive of Total, Europe‘s third-largest oil company after Shell and BP, since 2007 and spent his entire 40-year career there.

Patrick Pouyanne, the head of Total’s Refining & Chemicals division, and Philippe Boisseau, in charge of Supply-Marketing and New Energies, have been tipped as two likely candidates to replace him.

A descendant of a family of diplomats and business leaders, De Margerie was the grandson of Pierre Taittinger, founder of the eponymous champagne and the luxury goods dynasty.

Married with three children and highly regarded within the oil industry, he was known for his good humor.

Pierre Blayau, president of the supervisory board of French nuclear giant Areva, said, “De Margerie was a flagship personality, heard and admired all over the world.”

“He didn’t care about being politically correct. He was a real character,” added Tom Enders, the chief executive of Airbus Group.

He will be buried in a private ceremony at Saint-Pair-sur-Mer, in Normandy in northwestern France, two official sources said. Another public ceremony will then be held in Paris, added one of them.

Employees at Total’s headquarters remembered a man who never neglected to say “bonjour” when he popped down to smoke a cigar.

“He had a very human side, very close to his employees,” said Sylvie, who works in the company‘s human resources division.

De Margerie had taken over the helm of Total at a challenging time for the group.

Shortly after his nomination, he was taken into police custody for more than 24 hours over graft claims in deals with Iran. He also had to defend Total against allegations of corruption during the U.N. “oil-for-food” program in Iraq.