Actually only #5 and possibly #6 is "hardest evidence", don't you think? The rest is heresay and speculation.
The hardest evidence at hand seems to be -- 1. she was intoxicated at Carlos and Charlies 2. the Dutch kid was in a shoving match with some of her fellow students 3. she left with the Dutch kid and his Indian friends in a Civic 4. she was kissing with the Dutch kid in the back seat while they were parked by the beach 5. she never got back to the hotel 6. there is blood in the back of the Civic
1 and 2 seem to come from multiple students from her school
3 and 4 are admitted to according to the defense attorneys
5 seems to be the case, according to the security staff at the hotel. The trio said they dropped her off, and the two security ex-guards were under suspicion. However, it now seems most plausible that the trio never brought her back to the hotel.
6 seems to come from various sources. But we don't know who's blood it is yet. And if it is Natalee's blood, it may have resulted from either criminal or non-criminal circumstances.