A train passenger, detained in Colorado after other passengers became suspicious, was released Monday after the FBI check.
The man, whose name was not released, was taken off the eastbound California Zephyr about 20 miles (32 kilometers) west of Denver late Sunday after other passengers said they heard him talking about a bomb and a knife, authorities said.
He was released after questioning, FBI agent Rene VonderHaar said.
"I think what happened was not a miscommunication, but I think that it's one of those things that just escalated," she said. "With that said, we take all these things very seriously."
About 220 passengers were evacuated from the train and taken by bus to Union Station in Denver, the train's next scheduled stop. They reboarded the train there and continued eastward about 3½ hours after the original stop, Amtrak spokesman Marc Magliari said.
Magliari said he did not believe the passenger who was removed from the train reboarded. "I believe he made alternate travel plans," he said.
The man had a knife in his luggage, authorities said, but it was not clear whether he had access to it.
Authorities said a bomb-sniffing dog signaled an alert when it checked the man's luggage, but they said nothing suspicious was found.
"It could have been something spilled in the bag, but I'm not sure," said Gary Creager, a police commander in suburban Arvada, where the man was taken off the train.
The eastbound Zephyr leaves each day from Emeryville, California, bound for Chicago.