A 19-year-old man, the son of a police officer, was suspected just after the robbery.
"We have evidence that they were hidden there after the robbery," Frank told her.
One week after the robbery on June 23, 1967, the letters are opened and delivered to the police.
"She wasn't very calm a couple of weeks ago after the robbery," he threw in.
The thieves are shown shot dead by police after the robbery.
"The night after the robbery we had another bingo at the same place," he said.
"We rung him last night after the robbery and got no answer."
They were found more than an hour after the robbery on Friday, holding $21,000 in an alley behind the bank.
Nearly 10 months after the robbery, they have yet to make an arrest.
They plan to shift to London after the robbery with the money.