He said "compelling evidence" linked Mr Cowan to the planning and execution of the escape and getaway.
Mr Cowan said there was lighting at the courtyard at the front of the house but none beyond that.
The walk ended at a Ranger's centre and Mr Cowan said he immediately took his grandson to the toilet.
She said she kicked out at Mr Cowan and yelled at him to get off her before being forced outside.
BBC: Former Big Brother star Jason Cowan cleared of sex attack
"If the identification by Miss Lockwood is, or may be, a mistake, that would mean Mr Cowan is not guilty, " he said.
Mr Cowan said he had never been to the historic house before and was not familiar with the lay-out of its grounds.
Mr Cowan said anything that had occurred prior to that was consensual.
BBC: Former Big Brother star Jason Cowan cleared of sex attack
The woman - who admitted she was drunk that night - claimed she was attacked after she fell asleep in Mr Cowan's lodge.
BBC: Former Big Brother star Jason Cowan cleared of sex attack
He said Mr Cowan had agreed he bought the Ford Escort which is alleged to have been the getaway car, but denies being Mr Farndon's accomplice.
The prosecutor told jurors they had heard from a number of witnesses who said they saw a man matching Mr Cowan's description hanging around the hospital that afternoon.
Mr Cowan said they took a torch and joined about 20 people who turned up for organised event with a ranger and members of a bat society in attendance.
Mr Cowan, who was recovering from an operation for thyroid cancer, had gone on the organised walk with a group searching for bats armed with a torch as instructed.
And he said Miss Lockwood could have picked out Mr Cowan in an identification parade not because he was the gunman, but rather that she recognised him from the prison.
He said there was no evidence the list found in Scotland, which mentioned burning out a car and listed a number of "targets" in Cambridge, was written by Mr Cowan.
Mr Cowan ended up walking in the dark on a route that would inevitably take him to the ha-ha at a point where there was a drop of about 5ft.
He said he did not notice Mr Cowan and his grandson going to the toilet and, if he had, he would have given individual instruction on returning to the car park.
Mr Perrins said when police arrested them in Scotland, they found ammunition, instructions and a cleaning brush for the gun in the boot of the Escort, and a checklist Mr Cowan had prepared.
"The prosecution say that Mr Cowan fits that profile perfectly, and the prosecution say that you can be sure - all 12 of you, beyond reasonable doubt - that Mr Cowan was the gunman, " he said.
Mr Cowan, a former water quality manager who was 61 at the time, raised an action seeking compensation at the Court of Session in Edinburgh against the Hopetoun House Preservation Trust and trustees including the Marquess of Linlithgow.
Mr Perrins said mobile phone data placed Mr Cowan outside West Suffolk Hospital on the day of the hold-up, and his DNA was found on a balaclava and on the inside of a case which the prosecution say contained the gun.
Likewise, Mr. Cowan says that he tries to "build a big fence" around his first work hour in the morning at 7 a.m. to clear his thoughts, catch up on reading and manage email.
Mr. SCOTT COWAN (President, Tulane University): We want the vast majority of money that's given to the school system to go to the schools and the principals.
Alan Cowan, for Mr Ronald, told the court that a legal aid application had been made but a decision was not expected until March and sought to have a stay put on proceedings until then.
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