PORTLAND, Maine (AP) – The father of a Maine toddler whose disappearance generated national attention has pleaded not guilty to an unrelated assault charge. Justin DiPietro was initially absent from court Thursday, leading to the threat of an arrest warrant. But a police spokeswoman said he later appeared and entered his plea in the courtroom. The 26-year-old DiPietro was arrested July 6 for allegedly assaulting a former girlfriend in Portland. The disappearance of DiPietro’s daughter, Ayla Reynolds, remains unsolved. He reported her missing Dec. 17, 2011, from his mother’s home in Waterville. Ayla was 20 months old, and police say she’s presumed now to be dead. Police have called the case the biggest criminal investigation in Maine history.