I hear you, but after they searched his car and apt, they found something which allowed them to file charges of abduction with intent to defile....so if she went willingly which I'm not saying she neccasarily didn't, what do you suppose they found that allowed them to file those charges if not evidence h had altered her state of mind, or restrained her? They must have found something that gives them reasonable proof she didn't leave willingly with him.
They also found something that allowed them to then get a warrant for his apartment.
And if you remember (if you don't, go watch it again), Longo was angry when he mentioned that. He knew Hannah was hurt/dead. Or at least that this guy had very bad intentions with her.