Little is known of Lennie Dunn but he played a vital role in the Frank Mitchell case and ultimately contributed to Nipper Read's case against them, although it didn't result in the conviction Nipper was hoping for.
Lennie ran a stall on Whitechapel Market selling books, mainly soft pornography. Hence the nickname. He knew of the Twins, as everyone in the East End did at the time, but wasn't "on the Firm," although he was desperate to be. He wasn't part of the Mitchell plan initially but as the Escape Party drove into London a few hours after Mitchell had walked off Dartmoor, the safe house that Nobby Clark had promised in Priscilla Road, fell through. He got cold feet at the prospect of Mitchell sharing a house with his parents.
Charlie Kray knew Lennie Dunn as he drank with some of the Firm, and he also knew that Lennie's wife had left him and he lived alone in his flat in Barking Road. Lennie was thrilled at finally being involved in the Firms activities, he had arrived. He was paid £500 for his trouble and stayed at the flat throughout the 12 days, but was relegated to sleeping on his own sofa to make way for Mitchell and the minder that was brought in to keep an eye on things. He cooked and cleaned and generally looked after everyone.
He was there on Christmas Eve, Mitchell's last day in the flat. And helped pack his clothes when Albert Donoghue told Frank that he was going to spend Christmas in the country with Ronnie Kray. And in the end, it was Lennie Dunn who gave Nipper Read the whole story on Mitchell's escape and how it ended. Consumed with paranoia after the Krays were arrested in 1968, and after seeing a newspaper stand screaming out the headline "Krays: New Moves Today", Lennie convinced himself that he was about to be arrested so instead, he handed himself into the police and told them everything.