Taxi driver James Anderson tells the Missoulian the man was acting strangely when he picked him up at a Missoula coffee shop.
He says the man first asked to be taken to the University of Montana campus, but couldn't give Anderson a specific location. The man then asked to be taken to a hotel, but not before stopping to buy cigarettes.
The cab fare was $7.50, and Anderson says the man tipped him $5 as they arrived at the hotel. Officers then pulled up and surrounded the taxi with guns drawn.
Police allege the man earlier entered a downtown bank, told a teller he had a weapon and demanded money. No one was injured.
Charges have not yet been filed, and the man's name wasn't released.