(CNN) The FBI has joined the investigation into who stole a baby Jesus from a Haverhill, Massachusetts, nativity scene and replaced it with a real pig's head.

During a press conference Friday, authorities said this case may be treated as a hate crime.

"If our investigation leads us to think this person was motivated by prejudice towards a religion, it will be treated as a hate crime," Haverhill police Detective Robert Pistone said, according to CNN affiliate WCVB.

Authorities say a priest at Sacred Hearts Church, north of Boston, called them Christmas morning to report the nativity scene theft and switch.

Video from CNN affiliate WHDH showed the pig's head wrapped in plastic in the center of the manger, surrounded by Mary, Joseph and lamb figurines.

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