A murder suspect was arrested after his prayer for forgiveness was heard by police bugging his car, a court heard.
George Maben, 45, from Rosehill, Surrey, denies murdering 65-year-old widow Maureen Cosgrove, who was strangled in her south London home.
Mrs Cosgrove was dead at her Carshalton home in March, the Old Bailey was told.
Mr Maben, who had a relationship with Mrs Cosgrove's daughter, was held after police heard him say: "God, forgive me for what I have done."
The court heard Mrs Cosgrove's daughter Lucy, 34, was expecting Mr Maben's baby.
They had lived for a few months at Mrs Cosgrove's home but the arrangement had not worked out.
Prosecuting, Anthony Glass QC said Mrs Cosgrove was asphyxiated with a ligature in her kitchen after arriving home from the dentist on 24 March.
Mr Maben was filmed on CCTV taking a bus to Mrs Cosgrove's home and putting on gloves during the journey, the court heard.
Police placed a covert listening device in a Ford Focus used by Mr Maben and, on 9 April, he was recorded praying out loud.
In the recording, played to the jury, Mr Maben said: "Please God, help me... for me and Lucy eliminated from all police inquiries and everything's all right, please God help me.
"I just could not take it any more. Every single day, she was breaking me down. Please God will you forgive me? Please God, sorry."
Mr Glass said Mr Maben's words "could and should be interpreted as a confession to murder".
"Clearly, the relationship between the defendant and his girlfriend's mother had seriously deteriorated," he said.
"With her out of the way, the defendant could see a future for himself, Lucy, her children and the unborn baby, without the constraints imposed by Maureen Cosgrove.
"That is why he killed her and he said so in these few words."
The trial continues.