British couple break down in tears as they tell Spanish court how they witnessed killing of Jennifer Mills-Westley

A British couple have described the moment they saw a man calmly stab and decapitate a woman in the aisle of a Tenerife supermarket.

Kenneth and Susan Bennison were giving evidence at the trial of Deyan Deyanov, a homeless and mentally ill Bulgarian man who is accused of murdering a British grandmother in the resort of Los Cristianos on the Spanish island.

Jennifer Mills-Westley, a 60-year-old retired road safety officer originally from Norwich, was stabbed and then beheaded in a shop near the beach on 13 May 2011.

The Bennisons, who live in Warrington, broke down in tears as they described the attack, via videolink, to the provincial court in Santa Cruz de Tenerife.

Susan Bennison said that after hearing a "very strange noise" while shopping in the supermarket, she looked to her right to see a man kneeling on the ground and repeatedly stabbing a woman she had previously passed in the aisle. Asked by Deyanov's defence lawyer, Francisco Beltrán, if she could see the man's face, she answered "yes", adding: "He looked unclean, wild and he did not look human."

Her husband told the jury of nine that there had been no argument or exchange of words between Mills-Westley and the defendant, who, he said, had looked "quite calm" as he attacked her.

"We heard her gasp for breath," said Kenneth Bennison. "He withdrew the knife out of her neck and then put it back in again. That's when I got my wife out of the building."

Answering questions from Ángel García Rodríguez, prosecuting, he added: "I wanted to help but when he pulled the knife out of her neck I realised there was nothing I could do for her."

Police officers, who were identified only by their badge numbers at the hearing, also told the court of the chaotic scenes that greeted them when they arrived at the supermarket.

One said: "When I arrived I saw some of my colleagues running towards a kerb where a security guard was with a restrained person who was covered in blood on the ground. The security guard said they had seen a head, or something like that.

"When we took him to the car, people started to shout: 'Murderer', 'Kill him', 'Hang him'. My colleagues put him in the car and took him to the police station.

"Until then I had not seen the head but people were shouting: 'There is a head, there is a head', and on the kerb opposite there was indeed a head covered by a blanket."

The officer said that after he discovered the head he followed a trail of blood into the shop, where he found the body in a pool of blood.

Yiping Chen, who was working in the shop when Mills-Westley was killed, said Deyanov approached her and twice said: "I have cut off the head of a crazy girl."

It also emerged that police had dealt with Deyanov twice in the days before the attack. One officer who attended the murder scene said he had stopped the defendant about 10 days earlier in Los Cristianos after catching him throwing bottles at a shopping centre.

Another officer said he found Deyanov having a row with a man at a different shopping centre in the resort about a week before the killing.

Deyanov, 29, denies murder. Giving evidence on Monday, he told the court his actions are governed by the voices he hears in his head, which have told him that he is an "angel of Jesus Christ" who will create a new Jerusalem.

He interrupted Wednesday's proceedings by shouting "I am Jesus Christ" in Bulgarian as a police officer gave evidence.

Deyanov has been diagnosed with acute paranoid schizophrenia and has admitted he was a crack cocaine and LSD user. The prosecution is asking for him be sentenced to 20 years in a psychiatric unit.

The case continues.