Other mistake: In season 3 it's revealed that Mike Delfino's doctor at the hospital is Ida Greenberg's nephew. When Ida dies in season 4 her only distant relatives come from another state, and there's no trace of her nephew from Fairview.
Desperate Housewives (2004)
1 other mistake in show generally - chronological order
Plot hole: When Zach Young's grandfather died, Zach was said to be the sole heir of the fortune. However, Noah Taylor (the grandfather) had a daughter that appeared several times while Mike Delfino was looking for Deirdre. Where was Kendra Taylor while Zachary Young was spending Noah's fortune on dresses for Gabrielle Solis? Why didn't she claim her share? She simply disappeared.
Bree Van De Kamp: It's the age-old question, isn't it? How much do we really want to know about our neighbours?
Trivia: Teri Hatcher (Susan), Felicity Huffman (Lynette) and Eva Longoria (Gabrielle) are the only cast members to appear in every single episode of the series.
More questions & answers from Desperate Housewives
Answer: He was investigating the lead not the case.