A woman was strangled to death after a "heated argument" with a fellow resident of a set of community living flats, a court heard.
Zac Jackson killed Katy Sprague, 51, in the common room of the flats they shared on Coleridge Road, Cambridge, on 27 November 2019, jurors heard.
He later told fellow residents and an ambulance call-handler "I killed her".
At Cambridge Crown Court, Mr Jackson, 38, of Coleridge Road, has admitted manslaughter, but denies murder.
Prosecutor Stuart Trimmer QC said Ms Sprague and Mr Jackson lived at Denham Place, which provides accommodation for people with mental health issues judged to require some level of support.
Ms Sprague suffered from acute anxiety and had the mental age of a younger person, jurors were told.
Mr Trimmer said "she would, on occasions, shout and scream if she didn't get her way".
The prosecutor told the court that on the afternoon of the attack Mr Jackson had been due to receive an injection, however he told a health worker: "I'm going to murder you and I'm going to murder Katy".
Later that day, Mr Trimmer said another resident, David Barron, walked into the common room and saw the defendant in the act of strangling Ms Sprague.
Mr Barron saw Ms Sprague "on her knees on the floor" and told Mr Jackson to stop, but was threatened, jurors heard.
He left and later returned with another person, but they saw Ms Sprague unresponsive on the floor and Mr Jackson said: "I've killed Katy".
Mr Jackson then repeated that on the phone to the ambulance service, and later told police it was a "heated argument we had, I didn't mean to kill her", the court heard.
Mr Trimmer called it a "sustained" attack "continuing through the interruption... to the point of death".
The prosecution finished outlining its case and the trial continues.