Cold Case: A Perfect Day / Season: 3 / Episode: 9 (2005)

When a fisherman finds evidence of a young girl's death washed up onshore in New Jersey, the team reopens the 1965 case of an abused four-year-old child and examine the domestic violence that took place in her family's home, initially suspecting the mother. 
 
Both Lilly and victim's twin sister see her and the twins share an embrace. 
No arrest is made since the killer was already deceased.