A documentary film-maker known for rescuing children from squalid Romanian orphanages in the early 1990s has been shot dead following a dispute at his California home.
The San Diego County Sheriff's Department said neighbour Michael Vilkin had been arrested on suspicion of the murder of John Upton, 56, of Encinitas.
The Los Angeles Times said the shooting might have been the result of a property dispute.
After learning of the plight of Romanian orphans in 1990, Mr Upton publicised the brutal conditions and was instrumental in bringing around two dozen orphans to America for medical care and adoption.
His brother Michael told U-T San Diego that Mr Upton and Vilkin argued previously about trees.
Vilkin, in an interview conducted in county jail, told KGTV in San Diego he fired in self-defence after Mr Upton menaced him with a gun during a dispute over foliage.
Vilkin said he owned vacant property next to Mr Upton's home and the two men had a disagreement over trimming shrubs.
"I did not go to him," he told the station. "He came to me threatening and pulled a gun (on) me."
Mr Upton's work in Romania also gained the attention of influential activists, inspiring Virgin tycoon Sir Richard Branson and actress Jessica Lange to help rescue youngsters from Romania.
Mr Upton went on to create an online network of films about charitable causes.