According to investigators, the family had called 911 for an unresponsive infant, but left their home on Ditman Street before first responders arrived. They were headed to the hospital in a MedStar ambulance around 5:15 a.m. when the crash occurred.
The medical examiner's office has not yet determined the infant's cause of death.
Sources tell Action News the ambulance driver is the infant's 51-year-old grandfather, and a longtime employee of MedStar. Police say he is suspected of driving under the influence and is expected to face charges.
Surveillance video obtained by Action News shows the ambulance entering the intersection at Torresdale and Harbison Avenues, striking a car, hitting a pole, and flipping onto its side. The other vehicle then crashed into a building.
New video shows ambulance crash that left infant dead
"It's horrible," said Michelle King of Frankford.
"That's real sad. I had to walk up here to see it for myself," said Leon Starks of Wissinoming.
Police say the victims - a 33-year-old mother and her infant daughter, identified as Marian Harris - were thrown through the windshield from the force of the impact.
Both were taken to the hospital, where the baby was pronounced dead. The mother remains in critical condition.
Investigators say the grandfather was driving under the influence at a high rate of speed, without lights or sirens, and ran a red light before hitting a Honda Accord driven by a 25-year-old man.
"It was like several different noises, and I wasn't sure exactly what it was, and I came outside, and I just saw a bunch of police cars coming into the neighborhood," said Milton Street of Frankford.
Neighbors expressed heartbreak as they learned the details.
"So sad. It hurts my heart. I'm just praying for them," King said.
"I'm just sorry, and I pray for the family that they can get through this," Street added.