An 80-year-old man was hit on the head with an axe by his granddaughter before he was fatally stabbed in the neck and chest, a jury has been told.
Prosecutors said Rachael Flemington, 28, killed James Fish - known as Eddie - at his bungalow in Waltham, north-east Lincolnshire.
Richard Woolfall, prosecuting, told Sheffield Crown Court that Flemington bought an axe on Amazon and also acquired a number of knives before she went to her grandfather's house on the morning of January 29.
Mr Woolfall said: "It appears she hit him on the top of his head with the axe. It looked like with part of the axe head but not the blade.
"She then went on to use an eight-inch carving knife that she had purchased a few days before."
He said Flemington had walked from her mother's house to her grandparents' bungalow, a short distance away, and found Mr Fish alone, apparently opening a parcel that had been delivered that morning.
Mr Woolfall said the defendant had been living in Scarborough but had moved back to her mother's home in Waltham a few days before the attack.
The axe had been delivered to her Scarborough flat.
The prosecutor said she stabbed her grandfather three times, with one blow severing the jugular vein in his neck and another going through his lung and aorta.
The jury of six men and six women was told that Flemington, of Manor Drive, Waltham, is charged with murder but has been declared unfit to be tried.
They were told by the Recorder of Sheffield, Judge Jeremy Richardson QC, that this was not a normal murder trial which determined guilt or innocence, but a "trial of facts" in which their task was to determine only whether she "did or did not commit the acts charged against her".
Judge Richardson said: "In this case the defendant is under a disability. That is a decision that I have to make. I have already made that decision. She is unfit to be tried.
"There is no meaningful way in which she can participate in this case. She is in hospital. She is being treated."