A British backpacker in Thailand was raped by both her killers before she was murdered, police have said.
They believe three people were involved in the attacks on 23-year-old Hannah Witheridge and David Miller, 24, whose semi-naked bodies were found on a beach on the island of Koh Tao earlier this month.
Lieutenant General Panya Mamen told the Bangkok Post: "Two of the suspects raped and killed Witheridge while another one witnessed the murder.
"We're confident we have a very high chance of finding the suspects."
Two different semen samples were collected from Ms Witheridge's body, he added.
Mr Miller, from Jersey, died from drowning and a blow to the head, while Miss Witheridge, from Great Yarmouth, died from head wounds on Sairee beach in the early hours of September 15.
A bloodstained garden hoe, which is thought to be the murder weapon, was discovered nearby.
Officers have collected 200 DNA samples from people on the island - including more than eight Thai footballers - and the results are expected at some point this week.
The footballers, who reportedly threw a late-night party at the nightclub where the victims spent their final hours, are the latest to be questioned by officers investigating the murders.
Almost three weeks after the deaths police are no closer to making an arrest and are offering a reward of more than £13,000 (700,000 baht) in an effort to catch the killers.
The latest development in the probe comes as it emerged tourists in Thailand may be issued with wristbands in the wake of the murders to help identify those who run into trouble.
Party curfews and restrictions on where they can be held are also being considered, as well as the idea of introducing a "buddy system" - pairing tourists with a local minder.
Tourism Minister Kobkarn Wattanavrangkul said: "When tourists check in to a hotel they will be given a wristband with a serial number that matches their ID and shows the contact details of the resort they are staying in so that if they're out partying late and, for example, get drunk or lost, they can be easily assisted.
"The next step would be some sort of electronic tracking device, but this has not yet been discussed in detail."
Having consulted hotels over the identity wristband idea, she admitted it had already been met with some resistance.
"Most people welcome the idea, but some hotels are concerned that tourists may not want to wear the wristbands," she said.