Police sources believe the son of a Scottish millionaire found dead in the boot of a car over 70 miles from his home in California was murdered by a feared drug cartel.

Homicide detectives in the state are probing whether Adrian Bonar, 34, was targeted by the MS-13 gang.

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Bonar, son of Greenock-born restaurant owner Dr Brian Bonar, was found wrapped in tarpaulin in an abandoned Lexus near Anaheim.

Officers are now probing a link between the murder and MS-13, also known as La Mara Salvatrucha, formed by Salvadorian refugees in the 1980s.

Adrian, who was born in California after Brian and wife Linda Green emigrated to San Diego, served at least two tours in Iraq with American forces before being honorably discharged.

In July, ultra-violent members of the cartel were charged with hacking a rival gang member to death with machetes in a Southern California forest in what police described as a “medieval-style killing”.

US president Donald Trump previously branded the gang “monsters” and California detectives are reportedly following a line of inquiry suggesting Bonar was “collateral damage” from a dispute gone awry.

A source told The Sun: “It would appear Mr Bonar found himself at the mercy of some heavy-duty criminals.”

“Officers are still working on a motive but it’s no secret these people are happy to use extreme violence at the drop of a hat.

“It could be the case that he found himself as collateral damage in a bigger dispute.”

Mr Bonar was laid to rest at a ceremony on Monday, with a coffin draped in the stars and stripes.

Attendees, including former fellow military personnel, wore thistles in tribute to his Scottish roots.

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His sister Pauline Gourdie posted a tribute online as mum Linda, from Stewarton in Ayrshire, flew out for the service in the city.

Pauline, from Gourock, wrote: “My heart is breaking, yet bursting with pride that you were my brother. It’s clear you were not only loved by your family but by so many whose life you touched.”