The headmaster who has allegedly admitted robbing a gold shop and killing three people in Lop Buri two weeks ago lied when he told police he had dropped the stolen necklaces in a river.

On Wednesday after his arrest, Prasittichai Khaokaew, 38, said he dumped the gold jewellery, worth about 500,000 baht, he stole from the Aurora shop in the Chao Phraya river in Sing Buri province.

That led to police divers wasting eight hours in a futile search for the gold. 

Mr Prasittichai subsequently admitted the gold was hidden inside a strut supporting the carport roof at his father's house in Lop Buri.

Mr Prasittichai was arrested in Lop Buri on Wednesday morning on his way to Wat Pho Chai School in adjoining Sing Buri province. He is the school's headmaster. 

He allegedly confessed to the gold shop hold-up and to shooting dead three people, including a child, and wounding four others.