Other mistake: Lynette is talking to Susan about Zach's infatuation with Gaby. Susan asks how Zach can afford so many expensive gifts for Gaby, to which Lynette replies that he inherited his grandfather's money when he "turned 18, a month ago." However, in the previous episode, Zach reminds Gabrielle that he is two months older than John Rowland, who, it was mentioned, turned 18 in season 1, two years before.
Other mistake: When Lynette and Tom are waiting for their kids at the bus stop, the bus that drops off their boys says "Briarcliff Academy." The boys actually go to Barcliff Academy.
Answer: He was investigating the lead not the case.