Solnick is the assassin hired by Jimmy Calhoun on behalf of Landale to murder Grant Whitaker and his family.
Calhoun hires Solnick to eliminate the Whitaker family (Grant, his wife Rachel and his two children, Matthew and Theresa) in order to obtain land that belongs to Grant without anyone inheriting it. Solnick completes the task, but he decides not to kill Theresa because he "doesn't kill kids".
Later, at some point, Solnick is incarcerated because of some other job, not related with the Whitaker family.
Two years after ordering the family's murder, they discover that Theresa is still alive and have to hire someone else to take care of her since she is the legitimate heiress of her father's land. While trying to save her, Reese visits Solnick in jail and, after threatening to speak about the murder of the brother of one of Solnick's cellmates, questions him to find out the name of the person who ordered the job. However, according to Solnick, there wasn't any names, only the money. Reese later tells Finch that Solnick has been defending his honor in prison because criminals don't like people who kill kids. Reese suggests that word of this reached Landale and they realized Theresa was alive as a result.