A three-alarm fire that erupted in a vacant building on Wednesday on the southside of Quincy is believed to have been "incendiary in nature," and police say a juvenile is a person of interest in the case.

An off duty Quincy police officer noticed the fire at 649 State Street while on his way to work.

RELATED: Crews battle three-alarm fire in Quincy's southside

Based on information gathered during interviews and evidence, a preliminary investigation suggests the fire was intentionally set, according to the Quincy Police Department.

On Thursday, police and fire officers said they determined a "male juvenile" was responsible for the blaze.

Officers interview the minor who was then released to his mother's custody, police said.

Reports will be forwarded to the Adams County State's Attorney.