A former detective has said he would treat the disappearance of Jay Slater as a "murder inquiry" to ensure evidence was not lost within the first 24 hours.
Steve Gaskin said things are "not looking good" for the 19-year-old Briton who was reported missing in Tenerife last Monday.
Slater allegedly tried to walk back to his apartment via a mountainous area in the Rural de Teno Park - near the village of Masca.
It is thought he had missed the bus to reach friends at the south of the island.
Jay Slater went missing in Tenerife last Monday
PAGaskin - who was a detective chief inspector with the Metropolitan Police for more than 25 years - said that when a missing person's report came in to the police, he would decide to either treat it as a missing person's inquiry or a murder case.
He said that if he wasn't sure he would always opt to treat it as a murder.
"If we treat this like a murder from the outset, then if it turns out not to be then nothing's lost, we only have a few hours - people call it the golden hour, but really it's the golden 24 hours - to gather forensic evidence before it's too late," he told the Daily Mirror.
"I'd want to know what he'd had from breakfast. Why has a 19-year-old bricklayer gone missing, what was he doing there, I would want to know everything about him, who was the last person to see him, check all their backgrounds too, I'd be speaking to police in the UK, has he got a criminal record, here or in Spain, what do we know about him."
LATEST DEVELOPMENTS:
Slater is thought to have left an Airbnb apartment where he had stayed with two people he met at the NRG music festival at around 8am.
A "possible sighting" of him in the village of Santiago del Teide - which is around 7km from Masca - has now been shared online.
The father of three - who runs The Crime Lab with his wife, former detective Kate Gaskin - added: "There's a lot of speculation, but I just want to deal with the facts.
"I'd want to know who did he speak to, who has reported it, what they said, and I'd want to know the background of all these people too.
Urgent searches for Jay Slater have been carried out over the past week
PA
"Where is the CCTV, have any of these people got criminal records, the whole idea of this is to get a clear factual picture. And I'd want it as quickly as possible.
"The longer this goes on the more you're likely to suspect a criminal element. It's not looking good after this amount of time."
Today marks the eighth day of searching with teams focusing on three different areas - the Masca Gorge, La Vica, and Las Portelas, as well as the surrounding Masca area.
