A man who spent seven years in prison after being convicted of murder on the strength of an earprint walked free from the Old Bailey yesterday after the charges against him were formally dropped. 

For the second time this week, scientific evidence given at trial was exposed as fundamentally flawed. As in the cases of the bereaved parents whose children suffered cot deaths, the misleading expert evidence led to a life sentence for an innocent person. 

The prosecution offered no evidence yesterday against Mark Dallagher, 31, who was originally convicted at Leeds crown court in 1998 of the murder of 94-year-old Dorothy Wood in Huddersfield. 

Mr Dallagher, who will seek compensation for wrongful imprisonment, was convicted primarily on the basis of earprints found on the glass of the window through which the intruder had entered the house. The prosecution expert, Cornelis Van Der Lugt, told the court he was "absolutely convinced" that the prints were those of Mr Dallagher's ears. 

The case made legal history as the first in which earprints led to a successful prosecution. Norman Sarsfield, of the Wakefield crown prosecution service, described it as "a great step forward for forensic science". 

However, Mr Dallagher, who maintained that he was handicapped by an ankle injury at the time of the murder, had protested his innocence from the outset. 

He appealed against his conviction in July 2002 and a retrial began in June 2003. After 10 days, the trial was abandoned and Dallagher was freed on bail while crown lawyers further reviewed the case. Yesterday, they threw in the towel. A DNA profile obtained from the earprint proved that it was not Dallagher's. 

James Sturman QC, counsel for Dallagher, told the court that the original conviction "was a grotesque miscarriage of justice". Judge Sir Stephen Mitchell formally found Mr Dallagher not guilty and told him, "This most unfortunate saga at long last comes to an end." 

It is believed that the new DNA evidence obtained by West Yorkshire police implicates a different suspect. 

Mr Dallagher told the Guardian: "I've waited seven years for this day. I've spent six of those years in prison, protesting my innocence to deaf ears. This last nine months has been a terrible ordeal - all as a result of the prosecution's reliance on now-discredited expert evidence. 

"The police should now properly investigate the murder of Dorothy Wood so that her family can finally have justice". 

Ms Wood, a retired health visitor who was profoundly deaf, was found dead in bed at her home in Whitby Avenue, Fartown, Huddersfield, on May 7, 1996. She had been smothered by a pillow and was presumed to have been murdered by a burglar who gained access through a transom window above her bed. Because of a heart condition, Ms Wood slept downstairs. 

Forensic examination revealed earprints on the glass immediately below the window. West Yorkshire police sent these to Mr Van Der Lugt, a Dutch policeman. For more than a decade, he had taken a close interest in earprint identification and come to believe that each person's earprints were unique. He had no formal forensic science qualifications. 

Last night, West Yorkshire police and the Crown Prosecution Service issued a joint statement pointing out that when the re-trial was ordered, "the court of appeal made no criticism of the way in which the crown had presented its case at the first trial." 

During the new inquiry, the statement went on, "further scientific work has been undertaken using techniques not available in 1996, which had affected the way in which the earprint evidence, in isolation, could be viewed".