Michael Kirkland was the twin brother of DHS Agent Bob Kirkland.
Kirkland tells Patrick Jane that Michael was the closest family member he had after his mother left by suicide and his father died from alcoholism. Michael, according to Bob, became an alcoholic and got involved with Red John, and then went missing. Kirkland automatically suspected Red John killed him, even though his body was never found. Becoming a twin-less twin, as Jane sympathetically tells Kirkland, is one of the worst kinds of losses, which Kirkland concurred.