The grandmother of terminally ill Jacob Wragg said his death was the best news she could have had.
Gwendoline Richards, a 74-year-old widow, said: "He was not Jacob any more. He was just a shell."
Mrs Richards, of West Street, Worthing, was giving evidence on the fourth day of her ex-son-in-law's trial at Lewes Crown Court.
Andrew Wragg, 37, denies murder but admits manslaughter on the grounds of diminished responsibility.
Wragg, a former SAS soldier, smothered ten-year-old Jacob at the family home in Henty Close, Worthing, last July, claiming it was a mercy killing.
Jacob suffered with degenerative Hunter syndrome and would not have lived beyond his early teens.
Mrs Richards told police how Jacob's health had deteriorated rapidly in the two months before his death.
His symptoms were more pronounced, his face had become heavy round the jaw and his stomach was bigger.
She said: "His hands were like claws and he was unable to hold anything. He could not stretch his hands.
"He could only totter round at home on the tips of his toes. The rest of the time he was in a wheelchair.
"He had times when he would sit on the floor and shout when you tried to get him into his wheelchair if he did not want to get in it. His hearing had gone."
Despite operations, she said, Jacob probably would have died.
Mrs Richards was woken by police early on the morning after the killing and they told her Jacob was dead.
She told officers in a later interview: "To be honest, to hear this was the best possible news I could have had."
Mrs Richards told the court how Wragg and her adopted daughter Mary, 41, had a volatile 14-year marriage before their divorce, but both loved Jacob.
Her grandson, she said, was very poorly at times but rallied well: "He could not hear any more and consequently lost his speech.
"He sometimes got very frustrated if he did not get what he wanted and he would kick or something like that."
Asked how she got along with her son-in-law, Mrs Richards said: "Not very well. He was very quiet and withdrawn."
Even so, Mrs Richards loaned him £12,000 to launch a video delivery business - money she was still owed.
Mrs Richards loaned Wragg a further £2,600 so he could train and buy equipment for more security work he was planning in Iraq and the debt was paid back on the day of Jacob's death.
That lunchtime, she said, she went with Mary, Jacob and the Wraggs' healthy son George, seven, to a French market on Worthing seafront.
Jacob, she said, seemed "quite perky" and enjoyed a hot dog for lunch.
At 11pm that day, Mrs Richards was woken by a telephone call from Mary: "She sounded very upset. Mary asked if George could stay the night."
Mrs Richards said she met Mary outside her flat: "She was obviously very upset. She was crying.
"Mary came out of her car and came across to me in tears and said, 'I think Andy has killed Jacob'."
Police called on Mrs Richards at 1am and broke the news that Jacob was dead.
Mrs Richards told the court she had never heard Wragg or Mary talk about taking Jacob's life.
Earlier, the court heard how Mary Wragg told police soon after the killing that there were days when she hated her son and wished "it was all over."
In one interview she said: "It was just an awful thing for Jacob to experience."
Mrs Wragg said she felt Wragg wanted to save Jacob from further suffering as his condition worsened.
Mrs Wragg stressed she had been sympathising with Wragg's feelings but she never thought he would kill their son.
She said: "I was trying to sympathise with Andy. There were times when Jacob's life was difficult...but that does not excuse his murder."
She told officers how Wragg had been shocked at how Jacob's condition had deteriorated when Wragg returned from a tour of security work in Iraq.
She said during the interview: "Jacob was not there half the time. He was gone. I hate it too.
"There are days I hate Jacob and there are days I wish it was all over. It was frustration and pain."
She said she felt Wragg had wanted to "save Jacob from all the trouble that was going to happen."
She later agreed her attitude towards her ex-husband had changed: "I originally believed, after the shock of realising what had happened, that Andy had mistakenly thought Jacob's life was unbearable and he (Jacob) was suffering.
"I realise that is not the case. This was not about assisted suicide or turning off a life support machine."
Defence counsel Philip Sayers QC asked if she was now trying to make matters worse for Wragg.
She replied: "No, I just felt he did not understand Jacob because he did not spend time with him.
"Although Jacob had deteriorated, he was still able to enjoy life, no matter how difficult it was."
Wragg, she said: "Never had the right to take away what time he (Jacob) had.
"It was my opinion Jacob's life was worth living."
The trial was expected to resume on Monday.
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