A man has been found guilty of stabbing to death another man, who he believed had murdered his brother.
Stephen O'Rourke murdered Rocky Djelal on the anniversary of his brother Michael's funeral, a court heard.
In 2000, Mr Djelal was arrested and released without charge as part of the investigation into Michael O'Rourke's murder. No one was ever prosecuted.
Stephen O'Rourke attacked Mr Djelal at a playground in south London on 31 October 2018, the Old Bailey heard.
The 48-year-old had become obsessed with his brother's death in the weeks before the stabbing, jurors were told.
A day before the attack he sent out messages saying he was ready to kill, the court heard.
The messages said he was ready for his own Valhalla - a reference to Nordic mythology where warriors who are slain, live on after their deaths.
The court was told O'Rourke had been tracking Mr Djelal through the Southwark area over the course of the day.
Although unemployed, jurors were told O'Rourke had dressed like a labourer wearing a high visibility jacket, paint-splashed trousers and boots to blend in with the many workmen nearby.
He stabbed Mr Djelal, 38, in Southwark Park, in Rotherhithe and he died at the scene.
O'Rourke will be sentenced at a later date.