Jessica Logan is the deceased wife of Wyatt Logan.
Jessica Logan was killed in a mysterious accident in San Diego, California. One night, after an argument with her husband Wyatt Logan, she decided to stay out rather than going home. According to Wyatt, that was the night that she died. Other details are scarce. But we do know that there is also a portion of Lucy Preston's diary from the future that has an entry on Jessica Logan in it.
When Wyatt helped Garcia Flynn capture Benedict Arnold he promised that he'd give Wyatt the name of Jessica's killer. Wyatt cooperated with Flynn to capture Arnold. Flynn has revealed the name of Jessica's killer is Wes Gilliam, a man serving for the murders of two women San Quentin State Prison.
Later, Rufus Carlin and Wyatt steal the Lifeboat to prevent the conception of Wes and therefore prevent the murder of Jessica. Wyatt was successful in preventing the conception of Wes, but Jessica remains dead. This implies that Wes was not the murderer of Jessica.