One man’s normal may seem suspicious to someone else. In Charles County on Friday, a man told of becoming suspicious when he saw another man get off a motorcycle and enter a bank without taking his helmet off, authorities said.

Inside the Capital One bank at the Waldorf Market Place, according to the county sheriff’s office, the man in the helmet brandished a knife, then demanded and got money.

He then told an employee to accompany him from the bank, the sheriff’s office said.

The suspicious witness watched the motorcycle rider, still wearing the helmet, leave the bank with what the sheriff’s office described as a panicked employee at his side.

Suddenly, the man in the helmet dashed to his red Honda motorcycle and fled, the sheriff’s office said.

The witness realized that the bank had likely been robbed, and he got into his truck and followed, authorities said.

A call to the bank confirmed his suspicions and he began feeding information about the motorcyclist’s whereabouts.

Police showed up. The motorcycle crashed near Bison and St. Stephens drives. The suspect was arrested, the sheriff’s office said. They said they also found a knife and a bag of money.