State police said he was wrapped in a T-shirt, put in a plastic bag and discarded, a tough sight for first responders.
"Everybody that's been to that scene that was present who had to observe that has had a rough day," said Lt. Eric Hermick, of the Pennsylvania State Police.
Hermick said the homeowner was putting up Christmas lights when he opened the door to the crawlspace and discovered the baby in the plastic. He immediately called 911.
"When you seen this baby, it's not what everybody envisions as you see there's a baby that appears to be dead or (decomposed)," Hermick said. "This baby was in excellent physical condition. It still looked like it was alive at the scene."
Hermick said that the situation is developing but authorities have a suspect in custody.
"We're working with the coroner's office and forensic pathologist and the district attorney's office to see what we can do to move forward with charges," he said.
According to Hermick, the suspect is Robinson, the baby's mother.
WPXI was told Robinson has ties to the people who live in the home where her baby was found. Police now are trying to piece together what exactly happened leading up to his death.
"Laws protect mothers who have babies who don't want them," Hermick said. "They can drop them off at a police station or hospital. Here's a case here where, quite frankly, the baby looks like it was fine and just left to die."
The baby's cause of death wasn't immediately known. An autopsy will be performed Monday night.