Spanish investigators believe a German man suspected of killing his female ex-partner and eldest son in a Tenerife cave had planned the crime well.
The suspect, identified as Thomas Handrick, 43, is under arrest and due to appear before a judge shortly.
The remote cave lies between ravines outside Adeje, a small resort. The man’s youngest son, aged five, told locals he had fled from the cave.
“Everything indicates that this [crime] was planned,” Adeje’s mayor said.
In a statement carried on the Guardia Civil (police) Facebook site, Mayor José Miguel Rodríguez Fraga said (in Spanish) “the indications are that he had prepared it very well and that, had it not been for the little boy, we wouldn’t have found out about it, or found out God knows when”.
The boy’s description of what happened led police and volunteers to the cave, after a lengthy search. There they found the two bodies with severe injuries consistent with an assault.
Locals had found the boy on Tuesday evening, wandering distressed in the mountains.
A Dutch woman called Annelies translated for the boy and quoted him as saying his father had hired a car and taken the family off for what he called a picnic excursion.
Annelies has been looking after the boy at her home, the Spanish daily El País reports. He does not yet know that his mother and brother are dead.
Police traced the Volkswagen Caddy van, seized it, and arrested Mr Handrick at his apartment in Adeje.
On Thursday people in Adeje mourned the victims with a minute’s silence and held a banner protesting against gender-based violence.
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Reports say Mr Handrick put up a fight when police arrested him and he denied knowing that his ex-partner and eldest son were dead. He is being held by police in Playa de las Americas, near Adeje.
According to the little boy, quoted by Spanish media, Mr Handrick drove them to the mountains and parked the car near the cave where, he said, he had hidden Easter presents for them.
The boy said he had witnessed his father assaulting his mother and then seen her lying on the ground, bleeding heavily, Spanish ABC news reported.
The boy’s maternal grandparents are reported to be travelling to Adeje to look after him. The family are from Saxony-Anhalt, in eastern Germany.
Spain’s Socialist government – facing a general election on Sunday – is treating it as a case of domestic violence and has condemned it on Twitter. Deputy Prime Minister Carmen Calvo called it “a brutal sexist murder”.
The Canary Islands are especially popular with German and UK tourists.
A woman called Rosi told Spanish media how she had found the five-year-old boy “tired and all red-faced”.
In a video clip on La Vanguardia news website she said the boy had “gripped my hand, as he was anxious”. She contacted the Dutch woman, Annelies, who acted as interpreter.
Gender-based violence is a major issue in Spain following some high-profile cases. There was an outcry after five men accused of raping a young woman in Pamplona were acquitted a year ago, in a case known as La Manada (the wolf pack).
Ms Calvo said 18 women had been murdered by partners or ex-partners so far this year. She condemned the Adeje case, saying “we must stop criminal machismo”.