Booth's memory will probably be the central issue in the case. Dearlove, now 71, maintains his innocence.
"There was and is no doubt as to what medical condition caused the death of Paul Booth," Richard Wright, the prosecutor told the court on Monday, as the Telegraph reported. "He died because of a severe injury to his brain that had itself been caused by a fractured skull. The real issue then in 1968 as now nearly 50 years later in 2017 is what caused that injury?"
In 1968, Dearlove lived in Haverton Hill with his girlfriend, Carol Booth, and her three children, Paul, Peter and a daughter, Stephanie.
According to court testimony heard this week, Dearlove was physically abusive with all three. The court heard the children were locked out of the house on freezing nights, the Telegraph reported. Stephanie Booth claimed her mother's boyfriend would lie on top of her in bed and slap her if she cried.
Peter Booth testified Dearlove would "punch and kick" him and also held his head underwater in the bath. "He would keep me under the water until I was kicking," Booth told the court, the Mirror reported. "He would hide under the bed, then hold your ankles and pull you out so you banged your head."
On Oct. 1, 1968, Carol Booth frantically knocked on the door of her neighbor at Haverton Hill in the early evening, prosecutor Wright explained to the court this week, the Telegraph reported. The neighbor found Paul Booth unconscious on a settee. He had stopped breathing. David Dearlove was trying to resuscitate the toddler. A doctor was called, and an ambulance also arrived. The baby was taken to the hospital, where he died.
According to Wright, there were red flags that Paul had suffered injuries while he was in Dearlove's sole care. "The post-mortem found a large number of bruises of varying ages," Wright told the court. "They suggest he had been deliberately assaulted and physically mistreated over a period of time."
But Dearlove maintained the baby had died after accidentally tumbling off a bed and that the child sustained the bruises while playing. With nothing conclusive pointing elsewhere, the initial inquest closed with an open verdict - an English court ruling acknowledging suspicious deaths where the specific causes remain unclear. "No police action was taken against Carol Booth or David Dearlove and the case was effectively closed," Wright told the court. The couple broke up in 1970. Carol died in the 1990s.
Peter Booth remained haunted by his baby brother's end. At least twice, as an adult Booth asked police to reopen the investigation. But he never shared the details of what he had seen as a 3-year-old - not until he saw the picture of Dearlove and Paul on Facebook.
The image posted by Dearlove's son online enraged him so much he confided his secret for the first time in a cousin, Booth explained in court. She contacted police and set up a meeting in early 2015. Based on Booth's memories of his brother's death in 1968, police arrested Dearlove.
This week, Booth told the court he remembered creeping downstairs from his bedroom at night because he was hungry or thirsty, the Times reported.
"I went to the door that leads into the front room. It was ajar and I stuck my head through and saw David Dearlove and my brother Paul in there," he said. "I could see David Dearlove's back with his arms outstretched swinging Paul round. He swung round and caught Paul's head on the fireplace. He was holding him by the ankles. Paul was face up looking at the ceiling. There was a yelp, a scream and then my mam came through from the kitchen and I heard her shout, 'What is going on?'"
The witness continued: "David Dearlove had hold of Paul on the floor with his hands by his side. I ran back up the stairs. I was really scared, I got back into bed and just laid there until I went back to sleep. I could remember the sound it made, it was a horrible thud."
Booth told the court he stayed quiet because he feared Dearlove.
This week prosecutor Wright told the court that investigators analyzed the original post-mortem filings. The experts - including a neurosurgeon and neuropathologist - determined Paul's death was probably the result of a deliberate assault from high-force impact, not a fall from a bed, GazetteLive.com reported. The experts are expected to testify as the trial continues over the next three weeks.
Under cross examination, Dearlove's lawyer suggested Booth's memory may be "muddled" or his recollection could have been from a different night.
"No," Booth said at one point. "I remember what I've seen. All those things I've said in court today have been what I remember."