Michaela Conoby also told jurors at Leeds Crown Court how she went to the house on Berkeley Mount, Harehills, and shouted through the letterbox after sister Angela did not answer phone calls or reply to texts.
A police officer forced open to the door on May 20 this year and discovered Angela’s decomposing body in the same room where partner Peter Stalgis was sitting on a sofa in the dark.
Mrs Conoby told the jury she kept in regular contact with her sister and they had organised a surprise 60th birthday party for Stalgis in November last year.
She described how she became concerned on May 13 when Angela failed to respond to a text message and her mobile phone went to voicemail.
Mrs Conoby said she then contacted Stalgis.
She said: “I rang him and he answered and I said ‘I have not heard from Angela’.
“He said ‘her phone’s broken. I’m taking her next week for a new phone.’”
She described how Stalgis then told her that Angela was out shopping at Morrisons.
Mrs Conoby said she contacted Stalgis on further occasions to make arrangements to see Angela and he became “a bit stroppy”
The court heard Mrs Conoby sent Stalgis a text saying: “I am worried now. What are you up to?”
She told the court: “I knew something wasn’t right but I just thought ‘oh well I will deal with it tomorrow’.
“I just thought they had let me down and couldn’t be bothered.
“It was unusual because Angela would not have just ignored me.”
Mrs Conoby told the court how she dialled 999 after going to the couple’s home with her husband and knocking on the front and back doors.
She said: “I was there a good while. I was knocking and shouting through the letterbox.”
Mrs Conoby said she also dialled Stalgis’s mobile phone and could hear it ringing inside the property.
A police officer forced his way inside the house and found Stalgis sitting on a sofa in the dark, next to a nearly empty whisky bottle and with the television on.
Footage from the officer’s body camera has been shown to the court.
Stalgis can be heard repeatedly saying “I lost the house”, “she didn’t know” and “I’m sorry”.
There was a large kitchen knife near him on the floor and when the officer asked him where Ms Conoby was, he pointed and at the other side of the room the officer discovered Ms Conoby’s lifeless body.
The prosecution claims Stalgis carried out the violent attack after had failed to deal with financial problems that left the couple of the verge of being evicted
Stalgis pleaded not guilty to Ms Conoby’s murder at an earlier hearing and prosecutor Jonathan Sharp said the defendant claimed he had no recollection of killing Ms Conoby, nor the reasons why, despite earlier confessions to police.
The trial continues.