An unemployed Keighley man accused of murdering his stepson more than 23 years ago walked free from court today after no evidence was offered against him, prosecutors said.

Stephen Knox, 53, of Ingrow Lane, was alleged to have pushed two-year-old Mark Harrison down the stairs at his home in Leicester as the boy's sister Kerry, who was only three at the time, looked on in horror.

But today it emerged three expert prosecution witnesses could not agree whether the fall allegedly witnessed by Mark's sister led to the toddler's death on December 12, 1986.

This led prosecutors to offer no evidence against Knox on the third day of his trial.

The trial at Nottingham Crown Court had heard Miss Harrison was haunted by the memory of her brother's death but was told by Knox to keep it secret or face the same fate.

Peter Joyce QC, putting the prosecution's case earlier this week, said that hours after the alleged incident the toddler died from a brain haemorrhage caused by the fall.

The court heard the Crown Prosecution Service brought the case after Miss Harrison told counsellor Anthony Scarborough in January 2007 about what she supposedly witnessed 23 years earlier.

He went to police and the case was re-opened, despite a coroner ruling in 1987 that the boy's death was accidental.

During the trial, the court heard an injury to the back of Mark's head could not be explained by Knox's claim that the boy slipped and fell three steps while playing.

A spokesman for the CPS defended its decision to prosecute Knox.

He said: "This case involved the tragic death of a two-year-old child 23 years ago. It was a complex case to investigate and prosecute.

"When deciding whether this matter should proceed to court, the CPS concluded that there was a realistic prospect of conviction based on the eye-witness account and the expert evidence.

"As with all prosecutions, the case was kept under continuous review.

"As it became clear during the course of the trial that some of the expert witness evidence was not consistent enough to sustain a conviction, the only course of action available was not to proceed any further with the case."

A spokesman for Leicestershire Police said they were not issuing a statement following the collapse of the trial.