The suspect is identified as 35-year-old Humberto Guzman-Garcia, who has a last known address in the 300 block of Lake Road in Avondale.
According to District Attorney Tom Hogan, Guzman-Garcia randomly knocked on the front door of the victim's Avondale apartment around 3:30 a.m. on Sunday, June 10.
The child opened the door slightly and detectives say Guzman-Garcia allegedly flipped the upper latch and snatched the child as her parents slept.
However, her parents soon noticed she was not in her bedroom and her father went outside to look for her, only to find his daughter being sexually assaulted behind a shed, Hogan said.
"The father is looking outside and sees, about 50 yards away behind a shed that there is a stranger, a man he's never seen before, who has his pants down, and has his 4-year-old daughter on the ground," Hogan said.
The child reportedly told investigators, "A monster took me."
Guzman-Garcia ran away but he was allegedly found hiding out in an abandoned car and was positively identified by the father.
The suspect is a complete stranger to the family, Hogan said. Investigators say he admitted to the abduction and assault.
"This crime is every parent's nightmare. A monster comes out of the night, abducts your child, and sexually assaults her. This is proof that evil exists in this world," Hogan said.
Dawn Clark, who lives in the apartment complex, said Guzman-Garcia knocked on her door about two hours earlier.
"About one o'clock he was messing with the door handle to my apartment, and I happened to look out the peephole and I seen him," said Clark. "You could see he was drunk, and he just left."
Guzman-Garcia has been charged with kidnapping, aggravated indecent assault, attempted rape and related charges.
He was arrested, failed to post bail, and was remanded to Chester County Prison.
Due to the nature of the crime, investigators are worried there are more victims out there. Anyone with information is asked to contact Pennsylvania State Police Trooper Stefano Gallina at (610) 268-2022.