The shooting happened in Bang Chan district of Bangkok’s eastern suburb in front Rid Barber on Soi Suan Sayam 15.
Police inspected the scene last night and found three spent cases of 9 mm cartridges, and a bullet.
All the three persons shot were rushed to Sereerak hospital where they were pronounced dead before arrival.
Killed were Mrs Sirilak or Jay Muay Sae Hor, 46, Mr Mulloh Bin-umat, 45, owner of the barber shop, and an unidentified Cambodian male employee.
Investigation by police revealed that the gunman was Mr Tosaporn Pitakwatananond.
Before the shooting the gunman drove his Toyota van to park in front of the barber shop which is next to his house.
He then had a heated argument with Jay Muay over the parking area in front of his house. Mr Mulloh came out of the shop in bid to calm down the quarrel.
But the angry driver instead, drew out a 9 mm pistol, fired shots at Jay Muay and her Cambodian employee.
Mr Mulloh ran back into his shop to escape but was chased and shot inside the shop.
The gunman then drove off and escaped, police said.
Bang Chan police they suspected the gunman ran away and hide somewhere in his relatives’ houses.