Antonio Maffei Assassination Bug

Hi,
I am right now stuck in a part of game Assassins Creed 2. I need some information in clearing up this level. Has anyone till now is able to kill Antonio Maffei. I had tried to reach the tower where he stays and when I enter I saw nobody there. At first the map shows that Antonio Maffei is in that part but as I enter no one seems there. This is a bug actually. I had checked out this in some videos but this seems bug in the PC version. I need a solution for this.
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