The U.S. Coast Guard gave the all-clear Thursday morning after officials said they received a threat indicating there was a dirty bomb on board the Maersk Memphis in the Port of Charleston.  Brad Nettles/Staff

A phone call — possibly from a conspiracy theorist — prompted the shutdown of a terminal at the Port of Charleston Wednesday night. 

The Coast Guard responded to the Wando Welch Terminal in Mount Pleasant after a caller reported the threat around 8 p.m., according to Lt. J.B. Zorn.

The caller said a possible dirty bomb — an explosive with radioactive material — was in four containers aboard the Maersk Memphis.

The supposed plot was also outlined in a series of YouTube videos posted Wednesday.

The terminal was evacuated until early Thursday when the containers were scanned and declared safe.  

Zorn and other Coast Guard officials at first said the caller was detained for questioning, but declined to discuss the matter further or provide more information on the man's identity, citing the ongoing investigation.

The videos show two men, known for pushing far-right conspiracy theories, discussing the possibility of a threat on the Memphis. George Webb and Jason Goodman have racked up millions of views on YouTube discussing what they describe as political corruption.

In the video, Webb said he was told about a plot targeting Memphis, Tenn., before saying it might involve a ship by the same name.

Lt. Cmdr. Ryan Kelly, a Coast Guard spokesman based in Miami, said the man who reported the threat was detained by local authorities in Zanesville, Ohio on unrelated charges. A Zanesville Police Department jail officer confirmed to The Post and Courier a man named George Webb was arrested Wednesday night and granted $3,500 bail. The officer said she could not release further information, including what Webb was charged with and whether Webb was connected to the threat at the Port of Charleston. 

Several other calls to Zanesville police officials were not returned. Other authorities could not release further information on the investigation. 

FBI Supervisory Special Agent Donald Wood said he could not disclose much related to the investigation but did say "nobody was detained or arrested based on federal violations, or by the FBI" in connection with the threat. 

Wood emphasized the investigation is ongoing. 

In the video posted Wednesday, Webb spoke about his suspicions and claimed to have talked to authorities. He also mentioned being in Zanesville at the time. 

"I just got off the phone with the Coast Guard in South Carolina," Webb said in the video. "They were obviously very hesitant to call out all the dogs and call out all the radiation meters and all that without knowing who our sources are."

Webb went on to say his sources "exist within the Midwest" and didn't want to be named because they feared retribution from acting FBI Director Andrew McCabe.

Later in the video he spoke more about his sources and said "I'm not sitting here quoting some conspiracy theorist site."

He added "We are totally vindicated if there is uranium in the suite — anywhere on the boat, anywhere on the ship."

Hours later, the Coast Guard said the ship was clear.

Port and law enforcement officials said the incident, which locked down the terminal and spurred a safety zone on the Cooper River until 3:30 a.m. Thursday, showed their response plans worked.

The Coast Guard's reaction to the situation was born from "extensive training" and contingency plans it updates annually, Zorn said. More than a dozen people from multiple agencies swept the ship for radiation, and X-rays probed the four containers.

"I can't speak for everyone, but it went as well as these things go," Zorn said.

In a tweet Thursday morning, Jim Newsome, president and CEO of the State Ports Authority, thanked federal, state and local officials upon the reopening of the terminal.

Erin Dhand, a spokeswoman for the SPA, said in a statement the port was open with "minimal impacts to our operations.” One shift was missed, she said, but the work was expected to be made up Thursday.

The Memphis, which is homeported in Norfolk, Virginia, left Charleston on Thursday en route to Savannah, where it’s scheduled to arrive Friday morning.

David Wren contributed to this report.

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Reach Michael Majchrowicz at 843-937-5591. Follow him on Twitter @mjmajchrowicz. Reach Thad Moore at 843-937-5703 or on Twitter @thadmoore.

Michael Majchrowicz is a reporter covering crime and public safety. He previously wrote about courts for the Daily Hampshire Gazette in Northampton, Massachusetts. A Hoosier native, he graduated from Indiana University with a degree in journalism.

Gregory Yee covers breaking news and public safety. He's a native Angeleno and previously covered crime and courts for the Press-Telegram in Long Beach, CA. He studied journalism and Spanish literature at the University of California, Irvine.