San Juan firefighters were able to control the blaze early this morning but a second fire police say was intentionally set left the home in disrepair.
It all happened at a home off San Francisco Street in San Juan on Tuesday morning.
Action 4 News cameras were rolling as police questioned and then placed two men into the back of a police car.
Investigators told Action 4 News that they were arrested on marijuana charges but one of them is a suspect in the alleged arson.
Firefighters say it was difficult to get the fire under control because there was ammunition stored inside the vacant home that kept going off.
Once secured, firefighters started hosing down the already destroyed property.
Fire Chief Tirso Garza said the reason someone might've set the home on fire-- is still unknown.
The home was part of an investigation back in December 2010.
A teenage male accused the homeowner Ruben Rodriguez of sexual assault.
Rodriguez was charged with three counts of aggravated sexual assault for allegedly raping the 17-year-old.
San Juan police say they're not ruling out that this alleged arson could be related to that case.