A son murdered his elderly mother with a chainsaw at the home they shared and initially told police she had fallen on to the tool as he cut up pallets for their wood-burning stove.

Robert Owens killed 75-year-old Iris Owens, a retired history lecturer and charity worker, in the garden of their home in Caerphilly, south Wales.

Cardiff crown court was told that Owens, 47, dialled 999 after the attack, and when paramedics arrived they found Ms Owens lying on her back and her son with blood on his hands.

She had a laceration to her neck and head and a black eye. There was also blood on a wall and on a tree stump.

Christopher Clee, prosecuting, said Ms Owens had been spotted hanging out her washing in the garden just after 5pm on 3 May. A neighbour then heard the sound of a chainsaw. Owens called for an ambulance at 5.21pm, claiming: “My mother went mad. I was chainsawing some wood and my mother went mad.”

She was pronounced dead 20 minutes later. Owens was arrested on suspicion of murder at 6pm. He said: “I know, I’m going to jail. I can’t believe this has happened. I was just chopping wood. Why did this have to happen?”

The prosecutor said he later told officers: “I didn’t mean to kill my mother. I was chopping wood pallets and she fell off on to my saw.” But at a hearing in September he admitted murder. As well as attacking her with the chainsaw, Owens strangled and kicked his mother.

In witness statements read to the court, Owens was said to be close to his mother. One woman who knew them said he seemed “odd, but not scary odd” and sometimes acted “like a child who wanted attention”.

The court was told they began to live together after Ms Owens’ husband died. Owens had a drug problem and was found to have had heroin and cocaine in his body at the time of the killing.

Simon Laws QC, defending, said: “He accepts he used the chainsaw to strike his mother. There’s no attempt to minimise what he did, he is responsible for these injuries.

“He is devastated by what happened in those few moments of anger in the garden and must live with the consequences.” Laws said the relationship between mother and son had been “close, loving and supportive”.

The judge, Mrs Justice Nicola Davies, said she would retire to think about the case, and would sentence Owens on Tuesday.