Akradet Tankae was detained in the southern province of Ranong after his relatives contacted police and said they would turn him over, police said, adding the suspect confessed to killing Hanna Charlotta Bäcklund, 27, on Saturday.
Akradet is a sea gypsy, part of a nomadic community that wanders across Thai and Myanmar islands in the Andaman Sea.
He had fled to Myanmar to avoid arrest, but his father convinced him to return to Thailand and turn himself in, Phuket’s provincial police commander Decha Budnampetch told AFP.
“He was arrested at 1:00 am and initially confessed that he did it alone,” Decha said.
“He said he wanted to rape her, but when she resisted, he attacked her,” Decha said.
Bäcklund was stabbed to death on Saturday when she left her bungalow to take a swim alone on the usually quiet Mai Khao beach.
Akradet approached Bäcklund from behind and demanded sex, threatening her with a knife. As she resisted, Akradet stabbed her more than 20 times, according to a police statement.
Police later charged Akradet with premeditated murder.
In 2006, Akaradet was arrested for allegedly stealing cash and assets worth 5.2 million baht ($165,000) from a British tourist in Phuket. He was later released on bail and is defending himself at a local court.