That could have indicated pre-planning but by not having a consistent alibi he left himself wide open as the prime suspect. If he planned it ahead of time you'd think that would be the first thing he concerned himself with, but then again everything about this guy appears inconsistent.
Check out post # 103.
Yes, but the only way he could really line up an alibi would be to get another person to lie for him--to get a person to say he was with him/her at the time Laci "disappeared". He may not have had anyone he trusted enough to confide in.