Police in Bensalem, 20 miles (32kms) northeast of Philadelphia, said in a statement the 16-year-old suspect flipped the screen to show his friend the blood-covered legs and feet of an apparent homicide victim.
The friend told her mother, who called 911 shortly after 4pm on Friday. Officers from the Bensalem Police Department said they identified the suspect as Joshua Cooper.
When they arrived at the suspect’s address at the Top of the Ridge Trailer Park on the 1400 block of Gibson Road in Bensalem, Mr Cooper ran off out of the back of the trailer, police said in a statement.
Entering the property, they found a 13-year-old girl dead on the floor of the bathroom from a gunshot wound and evidence that “substantial steps” had been taken to clean up the crime scene.
Mr Cooper was apprehended in a wooded area on Newport Mews Drive and Groton Drive shortly afterwards, police said.
Mr Cooper has been charged as an adult with homicide, possessing instruments of a crime and tampering with or fabricating physical evidence.
The Philadelphia Inquirer reported that officers found a gun safe and a holster with a pistol missing in a bedroom, citing a police affidavit.
Mr Cooper reportedly told police that the shooting “was an accident”, according to the affidavit.
He said on the morning of the shooting, he had accessed his father’s gun safe by disabling the locks.
The 13-year-old victim was dropped off at his trailer, and the pair watched Netflix. At some point she went to use the bathroom alone, Mr Cooper told investigators, according to the affidavit.
Mr Cooper’s mother then terminated the police interview, The Inquirer stated.
He was denied bail during an arraignment on Friday and has been sent to the Edison Juvenile Detention Center, police said.
The victim’s identity has not yet been released.
Police praised the actions of the teenager who reported the video call to her mother.