It began just before 7 a.m. when the agent noticed the man coming off of the bus arriving at the station threatening another with a knife, CBS News reports.
The agent apparently ordered the man to drop the knife, but he didn't comply, and so the agent fired his gun, CBS says, noting the man was hospitalized in critical condition.
Pittsburgh Public Safety said only that they were investigating an incident at the Greyhound station downtown.
This is a developing story. Check back for details.
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