A public school pupil who attacked two dorm-mates with a hammer told another boy that he had been watching horror movies in the preceding days.

The 16-year-old denied being mentally ill and said he thought he was dreaming when he caused serious head injuries to two sleeping boys aged 15 and 16 at Blundell’s School in Tiverton in the early hours of June 9 last year.

One of the pupils who went to investigate noise from the attack at a boarding house said he sat down with the defendant in a matron’s room just after the incident, in which housemaster Henry Roffe-Silvester also suffered hammer wounds to his head.

The housemaster asked a senior boy to stay with the attacker and calm him down and they spoke about what had happened in the dormitory. It was the first account given by the defendant.

The other boy said he looked scared at first but became more relaxed after drinking a cup of water and he was able to ask him what had led up to the attack.

The defendant, now aged 17, denies three counts of attempted murder in a trial at Exeter Crown Court, where the jury have been told it is accepted that he caused the injuries but his defence case is that he was sleepwalking.

The court has been played a video recorded interview with another pupil who went into the dormitory shortly after the attack and helped give first aid to the injured boys.

He arrived after the housemaster had also been attacked and after running to fetch a first aid kit, was tasked by the teacher with removing the defendant from the scene and sitting with him.

The boy said he had tried to find out about the background to the attack. He said: “The attacker said he had been watching a lot of horror movies and had the hammers to prepare for a Zombie apocalypse.

“I asked him what caused these things to happen and he just sat there. I tried to calm him down and told him to take deep breaths and I told him some jokes. I said the kids were all right and were not going to die.

“I tried to get him to relax and gave him a cup of water. He calmed down and asked if he could take a shower. I asked him if he was stressed before what happened.

“He said he had been preparing for a zombie apocalypse and that was why he had the weapons and a Swiss Army knife in the room and the hammers. He said he needed them to protect himself.

“I told him he did not have to protect himself because there was no danger. I told him it was not real. There was no reaction from him. He appeared calm but distressed. I could see that from his physical features.

“He said he owed a girl money but did not elaborate. I asked him if he had mental health problems or was seeing a psychologist. He said no but also said he used to drink his own pee.

“It was such a strange event to all of a sudden have two really injured kids. To me the only logical explanation was if he was mentally ill. I asked him if was sleepwalking and he said he had sleepwalked when he was a kid.

“He said he was dreaming. That was the only thing he could think of. He talked about weird things which people do when they are asleep. He was relaxed when we talked about it.”

The witness told police he did not know the attacker’s name but knew him and thought he was anti-social and had heard him argued with his dormmates, one of whom told him ‘my roommate is crazy’.