Princip, like I mentioned above, just happened to be the trigger man, he was actually in the wrong place and when the previous attempts at taking the Austrain's life failed, the driver took a wrong turn down a street that Princip jus thappened to be waiting on. Princip was in the wrong spot, its by shear luck that that driver took a wrong turn. It was one big clusterf**k, they got lucky.
All I was trying to point out is that there definitely was a Serbian connection to the assassination of Archduke Ferdinand.
As you pointed out, it was by mere coincidence that Princip was eventually successful in carrying out his plot. He had indeed initially failed, but chance fell into his hand when the Archduke's driver took that wrong turn.