While living on the run, Lowell changed his name to River Baldwin. Michael investigated his father in the past and he knew that he was a wanted criminal. Still, he and Gloria vowed not to turn him in.
During his time evading capture, Lowell changed his name to River Baldwin.  Michael, who had previously researched his father's criminal history, understood that he was wanted by the law. Despite this knowledge, Michael and Gloria made a decision not to report their fugitive father.