Thai police are offering a reward of more than £13,000 to try and catch the killers of two British tourists found dead on the island of Koh Tao.
The bodies of 23-year-old Hannah Witheridge, from Hemsby in Norfolk, and David Miller, from Jersey, were discovered on a beach on September 15.
A bloodstained garden hoe, believed to be the murder weapon, was found nearby.
A group of Thai footballers are the latest people to be questioned in connection with the investigation.
Police colonel Kissana Phathanacharoen said a reward of 700,000 baht, roughly £13,300, is now being offered for information which leads to the arrests of the culprits.
The government in Thailand says it plans to install more surveillance cameras and better lighting in tourist areas following the death of Norfolk student Hannah Witheridge.
23 year old Hannah, from Hemsby, and her friend David Miller were killed on a tourist beach.
The Thai Deputy Prime Minister said he had ordered the improvements and he had also sent additional police and soldiers to help investigate the murders.
So far there have been no arrests in the case.
Hannah, who was 23 and from Hembsy near Great Yarmouth, was found murdered on the island of Koh Tao with David Miller who was 24.Read the full story ›
The father of the British man murdered in Thailand believes his son had stepped in to help his fellow victim when they were both brutally killed on an island.
Ian Miller said it was in his 24-year-old son David's character to help, and claimed that was probably the circumstance when he and Hannah Witheridge were murdered in Koh Tao a week ago.
He told the Daily Mail: "It has become clearer and clearer that it is quite likely David was stepping in to help a girl who was in trouble.
"That would be absolutely in his character."
The body of a holidaymaker from Norfolk who was brutally murdered together with a fellow tourist in Thailand has returned to the UK, her family said.
Hannah Witheridge, 23, was found with severe head wounds next to David Miller, 24, on a beach on the island of Koh Tao on Monday.
Her family said today (Sunday) that they had travelled to Bangkok on Tuesday to bring their "beloved Hannah" home and find out more about the investigation.
"We can confirm that we have now returned to the UK with our beautiful Hannah.
As a family we feel enormous relief to have Hannah back at home where she belongs.
We continue to work closely with officers to assist in the investigation and bring those responsible to justice.
Our family is broken and require time to grieve in private - as do Hannah's many friends. With the support of our fantastic family liaison officers we will make further statements as required and when we feel able.
As such, we would be very grateful for time and privacy to try and come to terms with our devastating news."
Meanwhile, police in Thailand said they are investigating new evidence suggesting that the murders may have been due to "sexual jealousy".
A spokesman for the Royal Thai Police said that the force was also looking into claims that the pair had a row with a Thai man in a bar before they were killed.
"We have discovered fresh evidence which could lead to a new suspect who may have had a relationship or one night stand with Hannah or one of her friends or David the night before they were killed.
We have asked the Metropolitan Police to go back and make enquiries of Hannah's friends on this matter.
The liaison officer here in Bangkok is working on getting that statement. The faster we get it, the faster we may be able to get the bad guy.
No lines of inquiry can be ruled out and we believe these crimes could have been motivated by sexual jealousy.
Police have been made aware of reports that Hannah and David had a fight in a bar with a Thai man before they were killed, but cannot confirm if they are true."
Post-mortem examinations revealed that Ms Witheridge, from Great Yarmouth, Norfolk, died from head wounds while Mr Miller, from Jersey, was killed by severe blows to the head and drowning.
Police in Thailand said they still have not "come up with the exact number of the suspects" following the brutal murders of two British tourists, but confirmed they are looking for more than one.
Six days after the bodies of Hannah Witheridge, 23, and David Miller, 24, were found with severe head wounds on a beach on the island of Koh Tao.
A spokesman for Royal Thai Police would not confirm that DNA from Miss Witheridge's body reportedly matched that of two Asian men.
Police in Thailand have admitted the investigation into the brutal murders of two British tourists, including Hannah Witheridge from Great Yarmouth, is proving "quite difficult" as they revealed they do not know how many people were involved in the killings.
Five days after the bodies of Hannah Witheridge, 23, and David Miller, 24, were found with severe head wounds on a beach on the island of Koh Tao, a spokesman for Royal Thai Police insisted officers are "working around the clock to find the culprits" amid fears the investigation has stalled.
Post-mortem examinations revealed Miss Witheridge, from Great Yarmouth, Norfolk, died from head wounds while Mr Miller, from Jersey, died from severe blows to the head and drowning. A bloodstained garden hoe, believed to be the murder weapon, was found nearby.
Police Colonel Kissana admitted it was "difficult to say" if the killers were still on Koh Tao and police were unable to confirm if there was more than one murder weapon.
We're working closely with local police, local people and local authorities. The deputy commissioner is in the area for two days in a row.
We can't rule out any possibility. We have not come up with an exact number of suspects.
Last night we conducted a crime scene reconstruction to get a sense of what happened.
It's quite difficult at the minute to identify the suspects
Police Colonel Kissana also said 150 officers had been deployed on the island and senior police officials had met Miss Witheridge's "deeply distressed" family.
The family of Miss Witheridge arrived in Thailand yesterday and had an emotional meeting with Thailand's deputy police chief, in which they were given updates on the investigation into her death.
The bodies of the two young Britons have been moved from a forensic hospital in Bangkok and arrangements are being made by the Thai foreign ministry for them to be repatriated, according to reports.
The family of a woman from Norfolk killed in Thailand at the weekend have arrived in the country.
Hannah Witheridge who was 23 and from Hemsby near Great Yarmouth was murdered along with another British tourist.
The Thai police force is facing growing criticism for the way it's handling the double murder.
Watch Kate Prout's report here.
Thailand's Prime Minster has apologised for suggesting that foreign visitors to its world-famous beaches might be unsafe wearing bikinis as the family of a tourist from Great Yarmouth who was brutally murdered at a Thai resort arrived in the country.
Relatives of Hannah Witheridge, whose body was found on a beach alongside fellow British victim David Miller, hugged each other as they prepared to meet Royal Thai Police at their headquarters in Bangkok.
Miss Witheridge, 23, and 24-year-old Mr Miller were found with severe head wounds on the island of Koh Tao on Monday.
In the face of mounting criticism, military ruler Gen Prayuth Chan-ocha said: "I apologise that I have spoken too harshly ... I didn't mean to criticise or look down on anyone. I can guarantee that Thailand is still safe ... I wanted to warn (the tourists) to be careful."
Earlier this week he had claimed that foreigners visiting the Southeast Asian country think "they can do whatever they want, wear bikinis wherever they like ... (but) will they be safe?"
His comments came as the investigation into the murders appears to have stalled with police having no suspects.
DNA discovered on the body of Miss Witheridge has been found not to match British brothers Christopher and James Ware, who had been speaking with officers.
And migrants, who had been questioned after bloodstains were found on some of their clothes, are no longer suspects after detectives revealed no matches were found between them and two sets of DNA found on Miss Witheridge's body and on a cigarette butt discovered near the scene of the murders.
Royal Thai Police had insisted they had found "strong evidence" in connection with the deaths.
A bloodstained garden hoe, believed to be the murder weapon, was found nearby.
More than 70 Thai police have been questioning migrant workers and tourists on the island, visiting hotels, bars, homes and businesses as they search for the killer.
Relatives of Hannah Witheridge, the young woman found murdered in Thailand, have arrived in the country to meet police.
Some of Hannah's family hugged each other as they prepared to meet Royal Thai Police at their headquarters in Bangkok.
Miss Witheridge, 23, and 24-year-old David Miller from Jersey were found with severe head wounds on the island of Koh Tao on Monday.
Tests carried out on a group of Burmese migrants questioned over the deaths have shown no DNA matches, police said.
DNA discovered on the body of Miss Witheridge has also been found not to match British brothers Christopher and James Ware, who spoke to officers.