Washington (CNN) -- Miami International Airport was shut down for several hours Friday after screeners spotted a canister inside the luggage of a scientist that eventually turned out to be "a legitimate experiment."
Concern about the incident increased greatly overnight when authorities learned that the 70-year-old scientist once spent time in prison nearly a decade ago for illegally shipping vials of deadly bubonic plague bacteria.
After a round of overnight questioning, the man was told by the FBI he was free to go. CNN is not naming the scientist, a U.S. citizen, because he was not charged in this incident.
The normally bustling airport was closed for more than seven hours when screeners spotted a metal canister in the man's luggage that "greatly resembled a pipe bomb," a U.S. government official said. The airport reopened early Friday.
Authorities say the man cooperated fully, telling investigators the canister was used for medical testing.
Authorities say the device was not explosive. When authorities opened the device, they found a secondary container within. Investigators said the container is used to transport dead bacteria samples.
"The container was a legitimate experiment," a U.S. government source told CNN.
The man's criminal history helps explain why authorities shut down much of the airport late Thursday, and why first responders in hazardous materials suits were dispatched to the scene.
Officials gave conflicting accounts of the man's travel arrangements, with one early report saying he arrived from Brazil, while later reports said the bag originated in Saudi Arabia, and traveled via London, England to Miami, Florida and that its final destination was Dominica via San Juan, Puerto Rico.
When Transportation Security Administration screeners found the device, they were examining the bag because it was to be placed on a connecting flight.
Most of the airport was closed for hours as a bomb squad team dealt with the canister. All concourses, except for Concourse J, were closed before the situation was resolved, police said.
Concourses E and F were evacuated at 9:30 p.m. ET Thursday after the item was found, said Greg Chin, a Miami-Dade Aviation Department spokesman. Authorities rerouted arriving flights to other parts of the airport.
Investigators from Miami-Dade Police, the Transportation Security Administration and the Department of Homeland Security responded, the Transportation Security Administration said in a statement. Airport roads were also closed "to ensure public safety," the statement said.
Debbie Casanova was one of many people caught in the traffic jam outside the terminals during the incident.
Casanova said she waited for her husband to come out of the airport for more than an hour and the wait continued even after she picked him up.
"We have been siting here for two hours," said Casanova, as she sat in her car with her husband, Roberto. "It is frustrating, but it is better to know everybody is safe."
CNN's Kimberly Segal, Carol Cratty, Cristy Lenz, David Alsup, Scott Thompson and journalist Rafio Storace contributed to this report.