GARYVILLE - A suspicious person caused a lockdown at a St. John chemical plant Thursday, forcing widespread concern in the small town on the east bank of the river near LaPlace. 

"It's all clear," Sheriff Mike Tregre told WBRZ.  

The sheriff said it was a case of mistaken identity.

Someone appeared to have been able to get through a security point at the Marathon facility around lunchtime, causing concern, though the person was later identified as a contractor.

There was no immediate threat and work returned to normal shortly after lunch.