TENERIFE cops ruled out the two British men Jay Slater went to an Airbnb with hours before vanishing too early, an ex-detective says.
Peter Bleksley said Spanish police have "rather embarrassingly" had to rewind some parts of the probe.
It means vital clues and chances may have been missed in the 17 days since Jay disappeared.
After going to a rave all night in Playa de las Americas, Jay travelled in a hire car to a remote Airbnb an hour away in Masca on the island's northwest with two men.
They arrived at the holiday let, Casa Abuela Tina, in the early hours before Jay left in the morning.
Ayub Qassim, who rented the Airbnb for £40-a-night, and his unnamed friend spoke to police after Jay disappeared before flying back to the UK the following day.
Qassim, who was jailed nine years ago for masterminding an operation to flood Wales with Class A drugs, claimed he took Jay back to the Airbnb as "his friends had all left him".
They have since been deemed "not relevant" to the case by detectives.
But ex-murder squad cop Bleksley believes police were too quick to dismiss the two men.
He told The Sun: "In the very early stages of the investigation the Guardia Civil almost dismissively said yes, we've spoken to the two men in the vehicle, and they are 'not relevant'.
"Well, if I'd been on this investigation I would have wanted all options to be explored to not rule anything out whatsoever.
"And to be able to say a sweeping statement like that so early on is very surprising.";
Bleksley said it was especially astounding given two plain clothes police officers were seen coming out of the Airbnb just days ago.
He has questioned the efficiency of the probe as they appear to be going back over all ground - meaning vital clues may have been missed.
Bleksley added: "So were these officers going back to the apartment over two weeks after Jay had gone missing to do some kind of forensic examination.
"If they were, that raises some very serious questions about the efficiency about the the thoroughness and about the competence of this entire investigation."
Jay's family were left "blindsided" when police abruptly called off the search on Sunday.
They insisted any new tip-offs and information would be investigated but halted the on the ground hunt.
Much of the almost two-week search was focussed on the mountainous terrain around Masca where Jay was last known to be.
Bleksley said: "I think the investigation has rather embarrassingly had to rewind itself to a certain degree by sending officers back to the Airbnb.
"And there are still questions that are being raised that have not been answered in any way.
"I think because the Guardia Civil so clearly put all their eggs in the one basket, in other words searching that mountainous terrain, that perhaps now they're having to rewind."
Bleksley said Tenerife cops may be reluctant to properly investigate the case as they fear it may hinder tourism.
He said: "This island is so heavily dependent upon tourism, is there reluctance on behalf of the police to actually delve as deep as they should into the murky world where we know there are drugs.
";We know that Tenerife, other Spanish islands and the Costas in southern Spain are heavily populated by criminals, organised criminals from the Russian mafia to local criminals, to British gangsters and more.
"Do they not want an accurate picture painted of what this area is like.
"And is that in part a reason why there may be some reluctance to delve as deep as I feel they should?".
It comes as Jay's family said they felt "kept in the dark" by Spanish cops.
Jay's dad Warren also questioned why his teen son ended up at a remote Airbnb with "two grown men".
Warren, 58, told The Sun: "My only question is, and this is where you start the investigation from, why did two grown men take a young boy to a valley to a bed and breakfast? I can't understand that.
"Why? Why? You need to ask them why and then start from there.”
Warren's questions come after a TV investigator helping the family claimed Jay left the Airbnb feeling “scared”.
Former detective Mark Williams-Thomas claims the lad did not want to return to the holiday let despite needing water and having little phone battery.
He told friends he “couldn’t do that” and that he was already 30 minutes walk away.
Mark also claimed Jay admitted swiping the a pricey Rolex in a Snapchat to pals while in a car on his way to the Airbnb
Despite the search being called off, Jay's family have vowed to keep looking for him.
Bleksley added: "Of course the heartbreak goes on for the parents and the family and friends."
He said if detectives in the UK were leading the probe, they would have likely shared more information with the family.
Ex-cop Bleksley added: "And I think we would have seen greater communication between the investigation and the public through press conferences to which the media would be invited.
"So there would be a regular flow of information as, and when the senior investigating officer deemed it appropriate, all of this seems to be lacking considerably here.
"I really have an awful lot of sympathy for Jay's parents, his brother, and others who loved him because they are reluctant to criticise the Spanish police.
"They want to keep them on board understandably. So it may be that they harbour concerns that they are not going to go public with."
