Andy Hall, an activist working with the defense team, said the two were found guilty on all counts. They face the death penalty but are expected to appeal.

Miller and Witheridge's battered bodies were found Sept. 15, 2014, on the rocky shores of Koh Tao, an island in the Gulf of Thailand known for its white sand beaches and scuba diving. Autopsies showed that the young backpackers, who met on the island while staying at the same hotel, suffered severe head wounds and that Witheridge had been raped.

The killings tarnished the image of Thailand's tourism industry, which was already struggling to recover after the army staged a coup just months earlier in May 2014 and then imposed martial law.

From the start, the case raised questions about police competence. Investigators faced a variety of criticism, starting with their failure to secure the crime scene, and then for releasing several names and pictures of suspects who turned out to be innocent.

After Britain's Foreign Office expressed concern to Thai authorities about the way the investigation was conducted, British police were allowed to observe the case assembled by their Thai counterparts.

Under intense pressure to solve the case, police carried out DNA tests on more than 200 people on Koh Tao.

The two migrants were arrested about two weeks after the murders. Police said the pair had confessed to the killings and that DNA samples linked them to the crimes. Both men later retracted their confessions, saying they had been coerced by the police. Police have denied the accusations.

One of the defendants, Win Zaw Htun, testified that he was tortured, beaten and threatened so he would confess. He told the court that police handcuffed him naked, took pictures of him, "kicked him in the back, punched him, slapped him, threatened to tie him to a rock and drop him in the sea," according to defense lawyer Nakhon Chompuchat.