A renowned London bagel baker broke down in court on Monday as he described finding his mother and sister lying in a pool of blood at the family home.

Mother-of-five Louise Cohen, 66, and Hannah Cohen, 33, were allegedly stabbed to death in the basement of their six-bedroom house in Golders Green, north London, on 11 August last year.

Louise Cohen’s youngest son, Joshua Cohen, 28, allegedly attacked them before changing his bloodstained clothes and walking out. He was arrested in nearby Golders Hill Park the following day and charged with two counts of murder.

Members of the Cohen family, who run a world-famous bagel bakery on Brick Lane in the East End, attended the Old Bailey for a trial of issue.

Judge Nicholas Hilliard QC ruled that the defendant, who sat in the dock, was unfit to stand trial. He told jurors Joshua Cohen was mentally ill and they would only be asked to decide whether he caused the unlawful deaths of the two women, and not whether he was guilty of any offence.

Giving evidence, his brother Nathan Cohen, 31, tearfully described how he found his mother and sister when he returned home after working at the bakery at around 9pm. He said had been keen to catch the second half of an Arsenal match and did not see his mother, who usually slept downstairs because of a knee injury.

“I wanted to catch the second half. I went upstairs to go and have a shower and as I was going upstairs I did glance over and did not see her there. As you go upstairs you can see into the kitchen and I noticed there was a lot of mess on the floor,” he said.

“There was red footprints to the end of the kitchen so I thought that was a bit odd. Then I came downstairs and went into the kitchen and I noticed there was lots of footprints. Initially I didn’t realise. I came to realise it was blood. It came to the end of the kitchen leading back to the basement.

“I was going, ‘What’s going on here?’. I followed [the footprints]. I saw my mum and sister lying on the floor in a pool of blood. First I was in shock and went over to my mum. I was tapping her going ‘mum, mum’.

“I turned to my sister. She was very pale. I straight away called 999. I said ‘you’ve got to come’. They said an ambulance was coming. They said, ‘Are they breathing?’. I said, ‘You’ve got to get here quickly. You’ve got to get here right now’.”

At the time of the killings, Joshua Cohen had been living in an annex at the bottom of the garden, while Louise, Hannah and Nathan stayed in the house.

Nathan Cohen told jurors his brother no longer had a key to the house and would not usually come in unless another brother was present. CCTV cameras at the home captured the sequence of events in August last year, the court heard.

Joshua Cohen allegedly walked to the main house and was let in by his mother while his sister vacuumed in the sitting room. He went into the kitchen followed by his mother and sister.

Prosecutor Sarah Whitehouse QC said: “Hannah and Louise Cohen were never seen again. In the next few minutes both of them were stabbed to death in the laundry room in the basement.”

Cohen emerged with blood on his head and legs, carrying bloodstained clothes upstairs, jurors heard. He was said to have changed into a red hooded top and grey tracksuit bottoms before leaving the house.

A postmortem examination revealed that Louise Cohen had suffered 13 stab wounds and a traumatic brain injury, most likely from multiple blows to the head. The head injuries were said to have been caused by a heavy object such as an iron or meat tenderiser. She also had injuries to her hands and arms that suggested she had tried to defend herself.

Hannah Cohen suffered a stab to the neck which severed her carotid artery. She would have died in seconds, the court heard.

The trial of issue continues.