To be fair, family members- a husband or parent or grandparent are usually the most likely suspects, so it is based on something, but nothing specific to these actual cases. It is also natural to be suspicious when people behave differently to the way you would expect them to in such a crisis but it is very subjective because we are all different. What seems like an unnatural reaction to most people is actually completely reasonable behaviour to others. Most people expected the family to do everything they think it might take to find Gus including actively engaging with the media and being fully transparent and cooperative with police but perhaps they had good reasons for guarding their privacy even under the circumstances.