The 23-year-old was electrocuted by a live rail before getting struck by an Underground train in Wimbledon while trying to flee from police, who attempted to pull over the cricketer in his car on suspicion of driving under the influence.
It was revealed at Maynard's inquest that the batsman had consumed large units of alcohol as well as taken cocaine and ecstasy.
"No matter how many times I go over that night, the fundamental thing is that everything we did, how we went out, the places we went, were things we'd done 10 times previously," Dernbach told the Daily Mail. "It was just another night out with a couple of really close friends.
"People say, 'Why didn't you know?' I understand that but hundreds of people came in contact with Tommy over his life and nobody knew. I don't know enough about drugs to understand what the signs are.
"If nobody else had an idea, why should I have done? I'd stood next to Tom and seen him do a drug test. It never entered my mind that he was taking anything."
The inquest ruled that Maynard's death was accidental.