Do I have to finish the tower quest before I can properly move on to the anatomy of a crime quest? When I go back into the city the young boy tells me that the detective wants to see me. he tells me about the death,I talk to Shani about performing a autopsy but from there I just can;t make any progress. I 'v e read walkthoughs but I can't proceed pass Shani telling me to meet her in the evening

Well, the only way to proceed is to meet her in the evening at her house. Also there is the possibility, That you already identified raymond as the bad guy. From here you can only bluff your way through a conversation with him (meaning lie to him about performing the autopsy). But it doesn't sound like you already progressed that far? Well, the tower quest is the very last quest in second chapter to finish. So, you don't need that one for the autopsy ^^