Two teenagers have been detained for the “sadistic” torture and killing of two kittens found cut open and hung in a wooded area in London.

A 17-year-old boy, who said he had dreamed of killing a human, butchered a small black kitten and hung it with rope near Ruislip, in the north-west of the capital, in May.

Judge Rai said the killings were “without a doubt the most awful offences against animals I have seen in this court”.

The judge said the boy’s actions were “extensively planned” and “clearly premeditated”, and told him that he had seemingly attacked kittens because “they have emotion and you would have power over them”.

The judge continued: “You said sorry in your [police] interview but reports also show that you struggle to show empathy and realise that the kittens would suffer.”

The boy, who cannot be named because of his age, had spoken of his desire to “get away with murder”, a hearing at London’s Highbury Corner magistrates court was told on Monday.

Notes on his phone read: “I really wanted to murder someone. Every day I was researching how to get way with murder.

“I have come close. I have killed cats to reduce my urges. I have skinned, strangled and stabbed cats.”

The teenager, along with a 17-year-old girl, pleaded guilty to causing unnecessary suffering to the protected animals by mutilating and killing them.

The pair also each admitted one count of possession of a knife at Ruislip golf course.

There was no reaction from the boy as he stood in the dock and was handed a 12-month detention and training order. The girl, who also cannot be named, was sentenced to nine months in custody.

Valerie Benjamin, prosecuting, told the court the boy’s “sadistic” actions showed a degree of planning in looking for animals, researching how to kill them and his “desire to go on to killing humans and how it would be to get away with murder and killing a homeless person”.

A month after their arrest, the pair were reported missing and were found at a bus stop with a bag containing clothes, toiletries and tins of tuna, the Metropolitan police said.

The boy admitted his role in the animal cruelty during his police interview, Benjamin said. He had no previous convictions.

She added: “He gave a prepared statement saying he was sorry for what he had done and took responsibility saying he was in a bad state of mind.

“He said he suffered depression, anxiety, hallucinations and self-harm.”