Hannah Witheridge, 23, from Great Yarmouth, Norfolk, and David Miller, 24, from Jersey – who was in the third year of a four-year masters degree in engineering at Leeds – were killed on the island of Koh Tao last September.
Their families have travelled to the nearby island of Koh Samui where Burmese migrants Zaw Lin and Wai Phyo, also known as Win Zaw Htun, stand charged with murder and rape.
On the first day of the trial, the court heard the bodies of Miss Witheridge and Mr Miller were found partially naked near blood spattered rocks.
The first policeman on the scene described getting a call at 6.30am that morning informing him that two bodies had been found on the beach.
“I found a man’s body lying on the beach with seawater lapping his body,” said Lieutenant Jakrapan Kaewkao, a witness for the prosecution.
“Then I found the woman’s body behind the rocks.”
He added that the bodies, both of which were mostly unclothed, were several yards apart and said Ms Witheridge’s bore signs of physical assault.
He also said the rocks were spotted with blood.
A doctor who examined the bodies of the two Britons is expected to be called later.
The investigation into the deaths has been marred by confusion and allegations of police incompetence.
The defendants are said to have confessed under pressure from local police shortly after the killings but have since retracted those statements.
Earlier, as he walked into the courtroom defence lawyer Nakhon Chompuchat said he hoped the trial would be a just one.
“We hope the truth will be revealed,” he said. “We hope the mechanism of justice in Thailand ... will have the same standards of international countries.”
While journalists were allowed into the small courtroom initially they were moved out to make room for others attending the trial including relatives and diplomats.
In statements issued today before the trial began members of both victims’ families spoke of the pain the deaths had caused.
Mr Miller’s family said: “The act which ended David’s life devastated our family and his friends.
“Just hours before he died David was talking to us with his usual enthusiasm, describing the beauty of Koh Tao and the friendliness of the Thai people.
“Over the coming weeks we hope to gain a better understanding as to how such a wonderful young man lost his life in such idyllic surroundings in such a horrible way.
“This pain will remain a part of us for the rest of our lives. We have borne our thoughts in silence as we have not wanted to influence any court proceedings, but simply want to see justice done fairly and openly.”
Ms Witheridge’s family said they were “united in grief” with Mr Miller’s loved ones.
They said: “Hannah was a beautiful person, inside and out, she brought a room alive just being there.
“She was fun, honest and loved life.
“Her bright future was brutally ended leaving those who loved her broken with no answers.
“Speculation, rumour and theory have been incredibly hurtful to our family and Hannah’s friends, making an already unthinkable time harder to bear.
“We of course want to see those responsible for the brutal murder of our precious girl brought to justice.”
Verdicts in the case are not expected until October.