The incident happened on 12 January, the Greater Cleveland Regional Transit Authority said. Another man can be seen sitting in an adjacent seat.
Eventually the RTA was alerted about the unaccompanied baby and ordered the train to go back.
Thankfully, that passenger stayed with the baby and managed to alert the driver and police.
He puts the baby into a seat with his bags before stepping outside to smoke.
The man was pictured running after the train but it was in vain.
But he was too late.
Turns out, the man underestimated how much time he had because shortly after he left, the train pulled out of the station. Inside the train vehicle, several people eventually gather around the baby.
Shocking video shows a father leaving his baby on a departing train..
The baby and the man were reunited.