Nicholas Mockford was shot dead outside a Brussels restaurant nearly two weeks ago but details have only now emerged

Police in Belgium are searching for a gunman and accomplice who killed a British oil executive on the streets of Brussels.

Nicholas Mockford, 60, was shot dead as he left a restaurant with his wife, Mary, nearly two weeks ago but details of the killing have only just emerged.

Mockford’s employer, ExxonMobil, on Friday said his death was not linked to his work.

Belgian detectives have appealed for witnesses to the shooting. Police said two attackers wearing crash helmets tried to grab Mary Mockford’s handbag, and then slapped her in the face during the attack. They said four shots were then fired at Mockford.

One witness told Belgian television he twice tried to resuscitate the victim before an ambulance arrived. “I heard a noise, ‘tack tack’, I thought that was bizarre and went outside to look,” he told Flemish television channel, VTM.

“There was a woman lying on the floor on the pavement on the other side of the road. She was crying ‘help, help’. There was also a man lying on the street, next to a car. [The] woman shouts out it was a white van.”

Initially witnesses believed Mockford had been run over by the van outside the restaurant in northern Brussels.

“Suddenly he stopped breathing,” said the witness, who lived next door to the restaurant Da Marcello where the attack took place. “I resuscitated him, he regained consciousness and then he became unconscious again. I resuscitated him a second time and then the ambulance arrived. Only then did neighbours realise the man had been shot.”

He said Mockford had what appeared to be bullet wounds to his chest and shoulder and he also saw blood on his head. Police found four bullet cases outside the restaurant.

Detectives initially worked on the theory that the killing on 14 October might have been an attempted carjacking, because witnesses saw the couple walking across the street to their 4×4 vehicle before the attack.

One Belgian officer was reported as saying the attack was a “very strange case” which had been passed to federal investigators.

Exxon Mobil refused to answer questions about the case. It released a statement which said the killing had nothing to do with his work.

“We were shocked by the tragic death of Nick Mockford, one of our employees a fortnight ago in Brussels. Mr Mockford was a department manager at our office close to Brussels, but we have no indication the incident was work-related.

“Our thoughts are with his family, friends and colleagues and we are supporting them as best we can at this very difficult time,” the company said.

The victim was reported to have been born in Leicestershire but had been living for a number of years in Belgium and Singapore. He is believed to have worked for ExxonMobil since the 1970s and was head of marketing for interim technologies for ExxonMobil Chemicals, Europe, promoting new types of greener fuel.

He and his wife, who is Belgian, had been married for 15 years. His three adult children from his first marriage live in Britain, according to reports.

The Foreign Office is providing consular assistance to his family.

The investigating judge imposed an order on police preventing them from releasing any detail on the case, which police said was not unusual in a serious murder case. As a result, initial news reports were sparse. But on Thursday, authorities switched course and decided to enlist the public’s help, releasing a brief description of the crime.