A killer knifed a pensioner to death in broad daylight just hours after telling authorities he would murder a stranger if they didn't section him, a court heard.

Cameron Davis stabbed Lorna England, 74, at least twice in a park as she walked home from a routine shopping trip to Lidl for some flour, a jury was told.

The pair, who had never met, tragically crossed paths in Ludwell Valley Park in Exeter, Devon, in February last year, the court heard.