Mary Shaughnessy's naked body was found face down in her bath by firemen called in by neighbours in Shoreditch, east London, Nigel Sweeney, for the prosecution, said.
The 55-year-old widow was extremely security conscious but there was no sign of forced entry, he told the jury. So police started investigating people who knew her, including William Forster, 33. His palm print was found on her recently cleaned bath although he had not been to see her for some time, and when DNA samples were taken from Mr Forster they matched semen removed from her body, it was alleged.
Mr Forster, Shoreditch, denies raping and murdering her on 27 December last year.
Mr Sweeney said Mr Forster was now in a wheelchair following a road accident the month after the murder. 'But he was very fit before and a blue belt in martial arts.'
The court was told that Mr Forster had been friends with Mrs Shaughnessy's sons since he was young, staying with the family regularly. Mr Sweeney said that shortly before Christmas he told one of her sons that he would pop round to see Mrs Shaughnessy.
The trial continues today.