Philadelphia transit police on Friday released a video showing an officer push by the throat an African-American man who was holding his toddler daughter, after he allegedly evaded a train fare of $2.25.The incident comes amid a national outcry over police violence against minorities and a renewed civil rights movement, sparked by police killings of unarmed black men in cities from New York to Ferguson, Missouri over the past year.An internal investigation has begun into Thursday afternoon's incident, Southeastern Pennsylvania Transportation Authority Police Chief Thomas Nestel III told reporters at a news conference where the video was shown."We can't endanger the lives of little kids over fare evasion. That's unacceptable. That's on me," Nestel said, adding that he had launched an aggressive campaign against fare evasion which had cut crime.In the train's surveillance video, a black officer can be seen talking for several minutes with the man, who is carrying his daughter on his lap, before attempting to arrest him.After the man continues to resist, the two scuffle and the officer pushes the man by the neck into the train wall, while the latter keeps holding on to his child.In a separate video of the incident taken by a bystander and published online by the Philadelphia Inquirer newspaper, someone can be heard trying to pay part of the fare before the man is handcuffed and taken off the train, still holding his daughter.Nestel said the officer, a 16-year veteran of the force who had faced no previous complaints, cited the fear of facing discipline if he walked away from the incident. He did not say what action the man might face.The father was charged with disorderly conduct, resisting arrest and fare evasion, Nestel added. The girl was handed over to her mother.The Inquirer said police identified the man as Ellis Smith, 20, adding he had no record of previous encounters with transit officers.