A world-renowned Texas scientist specializing in infectious diseases who was once charged with smuggling dangerous samples of plague bacteria into the U.S. was questioned by authorities after a suspicious item found in his luggage caused a massive evacuation at Miami International Airport Thursday night.

Dr. Thomas C. Butler, 70, was questioned by agents with the FBI and Miami-Dade police Friday after a suspicious item was found in his checked luggage by a MIA baggage screener Thursday night, sources told NBC Miami.

The suspicious item scare caused police to evacuate four of six airport terminals and the airport's hotel for nearly seven hours as a bomb squad removed the item for further testing.

The airport was fully reopened around 4 a.m., and initial tests on the item have come back negative.

Shortly before noon Friday, it was learned that Butler was released from questioning and won't be charged in the incident. Authorities escorted him back to one of the terminals at MIA where he's expected to board a plane to Puerto Rico, which was his destination Thursday night.

Butler was not identified by authorities at an early-morning press conference, where FBI Special Agent Michael Leverock said the man being questioned was not under arrest and was being "voluntarily interviewed."

"He's being very cooperative," said Leverock.

Leverock said the item was still being tested at a lab to determine what, if any, danger it posed.

"We don't even know if a crime occurred here," he said.

Sources told NBC Miami that Butler had been coming from Saudi Arabia when the suspicious item was spotted in his luggage as it went through customs.

Butler had been on the faculty at Texas Tech since the late 80s until his arrest in 2003 on charges of smuggling and improperly transporting the plague samples, as well as theft, embezzlement and fraud. Butler told police that 30 vials containing the samples had been stolen from his lab.

He was eventually found guilty of exporting the vials of plague and stealing research money. He was acquitted of illegally exporting the plague samples.

Butler spent nearly two years behind bars and lost his Texas Tech job, despite the protests of several in the scientific community who denounced his prosecution. His controversial story was even featured in a "60 Minutes" piece titled "The Case Against Dr. Butler."

He's currently listed as a faculty member at Alfaisal University in Saudi Arabia.