Continuity mistake: When Nora dies, Lynette stands up and strokes her hand over her chin, so a little blood stays on her chin. During the yelling scene of Lynette towards Carolyn, the blood on her chin changes constantly between shots.
Continuity mistake: In the scene where Carolyn shoots Lynette, Lynette is wearing high heels when she is originally shot. But when Lynette falls into Art's arms, she is wearing shoes without heels.
Answer: He was investigating the lead not the case.