Early Tuesday morning, someone cut a hole in the fence, poured gasoline onto a transformer and set it on fire.
The fire was discovered, and extinguished, before it caused any major damage.
One week ago, someone put a gas can - with wires attached - near a transformer. Police set up a perimeter around the facility but, before the bomb squad arrived, someone removed the gas can and disappeared through a hole in the fence.
The joint terror task force is now investigating because this is critical infrastructure. For example, on August 25th, a fire at this substation knocked out power to 20,000 PECO customers in Holmesburg, Mayfair and Tacony.
The terror task force is composed of the FBI, ATF and the Philadelphia Police.
At this point, investigators don't know what is instigating the arsonist. They haven't ruled out terrorism, but sources say that possibility is 'unlikely.'
Another theory - the substation is being targeted by a disgruntled current or former employee.
PECO is also worried about trespassers on its property. The substation is a high voltage area and anyone breaking in is taking a serious risk.
Anyone with information in this case is asked to contact the ATF at 1-888-ATF-FIRE.