Le virtuose

The coded note The Virtuoso receives at the start of the film reads:

"Once there was a worn and withered old man too set in his ways, bound by routine to have the fore-sight to understand that in all his seventy-six years he's always done the same thing, ate the same food, chose the same colors, won the same battles. His life a breathing pentagon: home, work, rest, eat, dream. From age eighteen he'd never questioned his lot. Until, the trinity... and the agony of realization that a life lived can never be re-lived."

The virtuoso is so careful, yet when he poisons the man in the motel he takes off his gloves when handling the glass. Which would leave obvious fingerprints.

Mistaken observation. He touched the glass once, swirling it to dissolve the powders he added. He put his glove on that hand before touching it.