Judge Ronald Stroyan directed the jury to find Trevor Thomas, 51, not guilty of murdering Susan Oliver last September after hearing of his 'honourable and praiseworthy' background, along with medical reports.
Mr Thomas, from Barking, east London, admitted manslaughter on the grounds of diminished responsibility and was remanded to a secure psychiatric unit. He will be sentenced on Friday after the judge has heard evidence on Mr Thomas's mental condition.
Georges Khayat QC, for Mr Thomas, told the court that on the day of the IRA bomb (10 April 1992) his ambulance was the first on the scene. Mr Thomas never recovered from seeing Danielle Carter die in front of him. 'The 15-year-old girl died literally in his arms. He had tried to resuscitate her. Afterwards he could not sleep, needed counselling and worried about what happened,' he said.
Five months later, suffering from depression, he shot Miss Oliver, 37, a nursing director, through the heart with a pump- action shotgun. The couple had been together for over 10 years.
Mr Khayat said that Mr Thomas had made several suicide attempts before the murder and after his arrest he was transferred to a special hospital because he tried to hang himself.