A man murdered his 19-month-old stepson almost 50 years ago by swinging him round by the ankles and smashing his head into a fireplace, a court heard.
David Dearlove, 71, denies killing Paul Booth, who died in hospital in October 1968.
At the time he claimed the toddler had fallen out of bed and hit his head at their home in Stockton-on-Tees.
Mr Dearlove, who now lives in Great Yarmouth, also denied manslaughter and cruelty at Teesside Crown Court.
The jury was told Paul Booth’s brother Peter, who was three years old at the time, claimed to have seen the murder through a crack in a door.
He told police on three occasions but the case remained closed until 2015, the court heard.
Prosecutor Richard Wright QC said there was no doubt that a fractured skull had been the cause of Paul’s death, but the jury needed to decide how it had happened.
He said: “The police interviewed Peter as a witness for the very first time in 2015. He had not been asked to give any account in 1968.
“What he said in that interview is what has led us here, 50 years on, to the trial of David Dearlove for the murder of his stepson Paul Booth.”
Mr Wright QC said Peter Booth told police his brother’s death “was not the result of an accidental fall”.
He added: “Through a gap in the door into the sitting room he had seen David Dearlove swinging Paul Booth around whilst holding on to his ankles and had watched as his stepfather smashed the little boy’s head into the fire surround, causing the fatal injury.”
The court heard that the boys’ mother, Carol Booth, who is now dead, had three children when she began a relationship with Mr Dearlove in early 1968.
Mr Wright QC said after Paul’s death, doctors had found multiple bruises of “differing ages” and he had suffered numerous “non-accidental injuries”.
The jury was told that Mr Dearlove allegedly abused Paul’s two siblings, which account for the cruelty charges.
The case continues.