Robert Trout III allegedly posted a video on his Instagram account threatening to travel to New York and "cause havoc on the subway."
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In the video, prosecutors say he brandished multiple firearms, including two semi-automatic guns with extended clips.
"If you're from New York City, do not take the train on Thursday evening," Trout said in the video.
He showed one of the clips holding 60 bullets while saying, "60 shots -- that's 60 people dead."
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Trout was arrested on Nov. 22, and has been in custody since then.
Trout made his initial appearance in federal court in Tampa, Florida, on Friday, and was ordered to be detained pending further proceedings.
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If convicted, Trout faces a maximum penalty of five years in prison.
MTA spokesperson Joana Flores released a statement on Sunday saying, "The NYPD and federal law enforcement authorities made clear prior to and on Thanksgiving that there were no specific credible threats to New York City, including to the transit system, and we are grateful to policing professionals here, and across the country, for the work they do to keep New Yorkers safe."