The case against a man accused of strangling and stabbing a woman 45 times has been described as too thin for a conviction.

Lawyers for Michael Humphries, a 43-year-old from Faringdon, who denies murdering academic Barbara Johnston in her North Oxford home in January, were summing up at Oxford Crown Court yesterday.

Julian Baughan, defending, told the jury: "This case is too thin for you to convict."

He accused the prosecution of ignoring the evidence of witnesses such as Helena Paivikki-Simons, a neighbour of Dr Johnston, who had reported a number of strange vehicles and people in Woodstock Close at the time of Dr Johnston's death.

Mr Baughan said: "Why no mention of Mrs Paivikki-Simons? Why no mention of two strange vehicles that morning? Why no mention of the intruder possibly coming out of Dr Johnston's flat? Because it does not fit with their case."

Mr Baughan told the jury that the prosecution had also been unable to link footprints and DNA samples found in the flat to Humphries.

Richard Latham, prosecuting, said the prosecution's case was based on safe inferences, not speculation.

He said the small trace of DNA could have been left by anyone in Dr Johnson's presence in the days before her death, and said Humphries had had time to dispose of the boots which may have left the prints in the flat.

Mr Latham said the defendant had been unable to explain why his van was seen on CCTV at the Woodstock Road petrol station just as Dr Johnston's credit card was used to withdraw £200 around the time of her death.

He said there were other unanswered questions, such as the whereabouts of the jacket he had been wearing that day, and of a bag of clothes seen in his van.

He also said Humphries' decision not to take to the witness box could be counted against him. Mr Latham said: "He has not given evidence because he can't. He can't answer the central questions in this case, the central questions that an innocent man could have answered in five minutes in the police station."

Judge Anthony King, summing up, warned the jury: "There is no direct evidence that the defendant caused the death of this lady."

But he added: "It is often the case that direct evidence of a crime is not available and the prosecution relies on what is called circumstantial evidence to prove guilt."

The jury are expected to retire and start to consider the verdict today.