ARVADA, Colo. -- The Arvada City Administration Building was evacuated Thursday morning after the driver of a car carrying a large propane tank abandoned the vehicle near the building.

It wasn't until hours later that police learned the security alert was not needed.

Police said someone saw a man grab a duffel bag and run from a 1986 Chrysler hatchback, after parking it near the city building shortly before 7 a.m.

Four hours later, police said the man had been located and the car was not a security threat.

"This seems to be a rather large misunderstanding," said Susan Medina, a spokeswoman for the police department.

According to police, the man said he had parked his car to wait for his girlfriend while she filed a police report on something.

The man apparently got tired of waiting, grabbed his duffel bag and left.

At the time, police didn't know why the car with the propane tank was abandoned.

City spokeswoman Maria VanderKolk said officials treated the situation "very, very seriously."

The Jefferson County bomb squad was called to to examine the vehicle. The Denver bomb squad was also called.

It took several hours for the bomb squad completely check out the car and the tank. First, a small tractor-wheeled robot was used to approach the vehicle and fired a shot into a side window.

Images from the robotic vehicle were relayed to a bomb squad van a short distance away.

Later, members of the bomb squad approached the vehicle in padded, green bomb suits. They placed something on the vehicle and opened the doors before moving away.

Detectives without protective clothing later approached the vehicle and began going over it.

The car's owner was finally located, and that's when emergency crews stood down.

The Arvada Post Office, next to the administration building, was evacuated during the morning as a precaution. Streets around the building were blocked off. About 70 people were working in the post office at the time.