If this syringe is involved in the case, it's hard to think it was in the bag KC brought out from WalMart (they don't just sell them over the counter without a script, do they?), although this is certainly something she might have gotten ahold of otherwise. Do you think CA would have had any reason to have them in the house?
If this syringe does have definite connections, it strenghtens the element of premeditation because it is not something readily available or normally on hand and would have had to have been procured far ahead of time.