From what I recall witnesses were able to establish that he owned the gun found at his residence.
Ballistics was able to determine that the bullet that hit the police officer could have come from the gun...although it couldn't confirm with 100% certainty because the bullet fragmented.
There isn't going to be DNA evidence with a shooting as the likelyhood of the killer bleeding all over a gun is small.
fingerprints can be wiped off a gun

stop watching CSI and join the real world.

Clearly your memory is screwy.

"From what I recall witnesses were able to establish that he owned the gun found at his residence."

He never testified and it was never made apparent that he owned the gun. The gun was found in the common basement of 65 Dayton street. Rivera testified that the man who shot DiPonzio told him to take it and the money and hide the gun. That doesn't establish Rivera owned anything.

"Ballistics was able to determine that the bullet that hit the police officer could have come from the gun...although it couldn't confirm with 100% certainty because the bullet fragmented."

Precisely. The bullet came from a gun that's as common as tooth picks. It's not a rare type of gun by any means and the ballistics person couldn't testify that this was the gun that shot DiPonzio--only that it might have been. So, that to me means no hard proof.

"There isn't going to be DNA evidence with a shooting as the likelyhood of the killer bleeding all over a gun is small.
fingerprints can be wiped off a gun"

That doesn't disprove the claim that the police were not able to find any DNA or fingerprints--a claim the police acknowledged as true in court.