It happened on just after 10:30 a.m. on the 1800 block of East Wishart Street in the Kensington section.
Neighbors told sister station Action News that they heard an explosion and saw smoke, and then heard screams coming from the child's home.
One neighbor covered the child's hands and rushed her to the hospital with her distraught mother. Officers intercepted their vehicle, at which time they transferred the girl to the police vehicle and rushed her to St. Christopher's Hospital, where she was admitted in critical condition.
"I see the little girl, blood all over her body missing two of her fingers," neighbor Margarita Artiaga said. "I said, 'Oh my God.'"
The girl sustained serious injuries to both hands, as well as cuts to her chest and face, and burns to her eyes.
"It was like a loud boom, it was so loud, I heard it in the back room," neighbor Judith Sierra said. "There was smoke coming out of the house. Then the neighbor was pushing the door real hard to get to the little girl."
At a news conference on Monday, police said their investigation revealed that the girl's father purchased two illegal explosive devices the previous night from a man on the street.
According to police, the father exploded one of the devices and left the other device on the mantel inside the home.
On Sunday morning, the girl was left home alone, and that's when police say she picked up the explosive device. Police say they believe the girl lit the device, leading to it exploding in her hands.
Detective Tim Brooks of the Philadelphia Bomb Disposal Unit said devices similar the one that exploded in the girl's hands are illegally made, and by definition are improvised explosive devices, therefore they have no quality assurance.
Detective Tim Brooks is the Philadelphia bomb squad shows what device may have looked like. He says many of these devices are illegally made and therefore have no quality assurance. Some may detonate without even being ignited. @6abc pic.twitter.com/zQQgFdS5j1— Jeff Chirico (@JeffChirico) July 1, 2019
These devices are considered inherently dangerous, as any bit of friction, heat or a slight bump can cause the device to detonate. M-80s, M-100s, M-250s are all considered illegal.
The ATF's website states an M-80, only 1.5 inches long, can damage fingers, hands and eyes.
The girl remains in critical condition.
Police say charges may be filed against the girl's father. Investigators are also looking for the man who sold the explosives.
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