The father of a missing Maine toddler whose disappearance drew national attention is facing a charge of domestic violence assault. Portland police say Justin DiPietro of Waterville was arrested at 11:15 p.m. July 6 after a police lieutenant saw him grab and push a woman on Spring Street. Officials identified the 25-year-old woman as DiPietro’s former girlfriend and say she was not injured. DiPietro’s 20-month-old daughter, Ayla Reynolds, has not been seen since she was reported missing Dec. 17, 2011, from DiPietro’s mother’s home in Waterville, where DiPietro lived. Police have called the case the biggest criminal investigation in Maine history. DiPietro, who is free on bail, could not be reached for comment. His previous cellphone number is no longer in service, and a new number in his name could not be located.