William LaMontagne, Jr.

William LaMontagne, Jr is a minor character in Criminal Minds.

Background
Detective LaMontagne was first seen in "Jones" as a New Orleans detective investigating a serial killer case which had initially belonged to his father, who had been a detective before unfortunately being killed in Hurricane Katrina. The killer was believed to have suffered the same fate but when evidence to the contrary arose, Detective LaMontagne took over the case using the work his father had done and a single word carved on the wall of his father's home, left as a clue. Detective LaMontagne called in the BAU to assist him and they were ultimately successful in capturing the murderer.

Relationship with JJ
In "Jones" we first see the attraction between Jennifer Jareau and LaMontagne. In "In Heat" it is revealed that they have been involved for over a year and in "The Crossing" we discover JJ is pregnant; in the season three finale "Lo-Fi" we discover that LaMontagne is willing to give up his job in New Orleans to raise the baby with JJ and that he has asked her to marry him.