Adrian Bonar, 34, was found wrapped in tarpaulin by the side of a road in Anaheim, California, around 75 miles from his home.
His father is Brian Bonar, 72, originally from Greenock, who owns a restaurant business in America.
It is understood police were preparing to remove the car when Mr Bonar's body was discovered.
He was a former US Army soldier who served in Iraq and is thought to have been married with children.
His funeral was held on Monday, attended by his mother Linda Green, 59, who lives in Stewarton, Ayrshire.
Mr Bonar's sister, Pauline Gourdie, 48, from Gourock, has taken to social media to say her brother's killers deserve to 'rot in the sewers of hell'.
Friends have set up the Adrian Bonar Foundation in his memory, to support former soldiers suffering from post-traumatic stress disorder and drug abuse.
An investigation is underway into his death.