Just a few thoughts this morning regarding the lights/luminol/etc.
In CSI shows they walk in and start spraying away. It is a great tool, but can also destroy evidence, so it is used with caution. They don't just walk into a room and start spraying away. Luminol is a mixture of hydrogen peroxide and sodium hydroxide which when mixed together reacts with several things llike iron (in blood) and copper and creates a chemical energy reaction which throws off a glow. This glow only lasts for about 30 seconds before the reaction is over. A luminol room needs a dark room to show, but does not have to have a special light to work.
Black lights/UV lights/ALS lights are also used to uncover what can't be seen by the naked eye. A whole lotta things show up under this type of light. Things that matter and many that don't.
I would not say that just because they were in the house yesterday means that they didn't do it in the beginning too. It's quite possible they were in there looking to see if there were any changes.... It would be surprising to me if they hadn't checked for blood/bleach/fluids in the beginning. There is a reason they were there yesterday. We'll just have to wait to see why.