He seemed to possess a strange ability to speak to the dead through their crime scene photographs. This could have all just been his schizophrenia given the symtoms of that disease. In any case his obsession with the case of John Doggett's son's murder gave him crucial knowledge of the perpetrators. So it is possible the crime scene photos of Luke Doggett actually spoke a message to him OR his obsessiveness from being schizophrenic led him to notice details lost to others.