Proof of Hamas' involvement in Nahal Oz attack

The gullible Western press happily reprints claims of responsibility for terror attacks, like this example from Reuters:

Fighters from three factions -- not including Hamas -- infiltrated the terminal.

The stories go on to say that Israel holds Hamas responsible, but the impression one gets from these stories is that there is no evidence behind that accusation, and that Israel is trying to gain political points.

However, there is clear proof that Hamas was directly involved in the attack. And even the Reuters article mentions it a couple of paragraphs later:

Hamas said it pounded the area with mortar bombs and machine guns during the operation, which one of the groups involved, the Popular Resistance Committees (PRC), dubbed "Breaking Zionist Arrogance."

Before and during the attack, Nahal Oz was bombarded with the worst mortar attacks in memory. And Hamas happily takes credit for the barrage in Arabic on its Al Qassam website (autotranslated):

Qassam Brigades resume bombing site "Nahal Oz" Zionist Qassam rocket (2008-04-09)

Qassam Brigades Tguens Zionist soldier near "Nahal Oz" The Zionist enemy recognizes affect it (2008-04-09)

Bomb-Qassam Brigades, a gathering of the mechanisms at the gate "Nahal deficiency" Qassam rocket (2008-04-09)

Bomb site Qassam Brigades "Nahal Oz" Zionist fired Qassam (2008-04-09)

A major part of the terror attack was the cover provided by this huge escalation in mortar fire. Which means that Hamas is just as involved in this terror attack as Islamic Jihad, Fatah and the PRC.

It also shows, yet again, that these "competing" groups work together quite well, so much so that some will take credit in order to take the political heat off of Hamas.

When Israel says that they hold Hamas responsible, they know how these groups work together, and they know who is calling the shots.