Defendant Barry George could not have shot dead TV presenter Jill Dando because he did not have the intelligence to carry out such a "perfect crime", a jury was told on Tuesday.
George, described by his defence as "the local nutter" with personality problems, had an IQ of 75, putting him among the lowest 5 percent of the population.
He could not have "meticulously planned . carefully prepared . the thoroughly professional" killing of the "Crimewatch" presenter, said William Clegg, defending, in closing comments at the Old Bailey.
He did not have the skills, ability, motive nor expertise to carry out such a crime, Clegg added.
Dando, 37, was shot at point blank range with a gun pressed against her head on the doorstep of her Fulham home, in west London, in April 1999.
Clegg suggested the gunman may have laid in wait in the overgrown bushes at Dando's home and pressed the gun close to her head to muffle the sound of the blast so that no one would be alerted.
"You may think that the killer would have known what he was doing," he told the court.
"He had planned it, executed it with clinical efficiency and put into place an escape plan that included leaving behind no trace or clue to connect him with the crime.
"Make no mistake, this killer managed to shoot a woman in broad daylight in the front garden of her home in a busy suburban street without making a sound, and escape undetected. That was no stroke of luck, that was meticulous and careful planning.
"It was, you may think, the perfect crime.
"It certainly defeated one of the biggest manhunts that this capital city has ever seen for over a year.
"There were, it seems, no leads. So who was this master criminal who outwitted Scotland Yard? Our Barry - what do you think?"
The court had earlier heard how George was obsessed with celebrities, adopting the names of various entertainers.
He had also stalked women and taken thousands of photographs of them as they walked home.
The defence accepted George had stalked and frightened women in the area, but said that did not make him a killer.
"It is perfectly true he follows women every day, hundreds and hundreds in a year, but he has not shot them dead."
None of his large collection of newspaper clippings, which included stories about celebrities, featured Dando, Clegg noted.
George, who lived near Dando, was originally tried for her killing in 2001 and is now nearing the end of a retrial.
He denies murdering Dando five months before she was due to be married. He did not give evidence during his trial.
The case continues.
