The Palestinian Center for Human Rights on Wednesday condemned the Israeli military's decision to close the case of the Samouni family without initiating prosecutions.
The 2009 shelling of a house in Gaza killed more than 20 members of the Samouni family, but Israel decided Tuesday it did not constitute a war crime and that the civilians had not been targeted purposefully.
The killing occurred during Israel's three-week war on the Hamas-ruled Gaza Strip, and was deemed an intentional attack on civilians in the UN-sponsored report by South African justice Richard Goldstone.
Witnesses at the time said that on Jan. 4, 2009 Israeli troops had ordered about 100 civilians in the Zeitun district to enter the house and stay there, out of their way.
But the following day the house was hit by Israeli shells and collapsed, killing the members of the extended Samouni family.
The Palestinian Center for Human Rights called the series of attacks "one of the most horrific single events" during the course of Israel's assault, and said it included "the willful killing of 27 civilians."
"The Israeli military’s claim that allegations of war crimes committed in relation to the Samouni case are ‘groundless’ simply defies belief," PCHR said, noting it filed dozens of criminal and civil complains.
The rights group says "this incident emphatically underlines the flaws inherent in Israel’s investigative system, which have been documented in detail elsewhere," and endorsed by UN experts.
"Simply put, this system comprehensively fails to meet international standards."
It added: "The decision to close the Samouni family case clearly indicates Israel’s genuine unwillingness to uphold the rule of international law, and highlights the urgent need for recourse" in international courts.
Reporting on Tuesday on the decision not to take legal action, Israel's Channel 10 television described the shelling as "the most serious operational mishap" of the Gaza war.
After an investigation into the shelling and allegations of war crimes, the Military Advocate General "found the accusations groundless", the military said in a statement.
"The Military Advocate General also found that none of the involved soldiers or officers acted in a negligent manner," the military said, but added it was making changes to "ensure that such events will not happen again."
Israel launched the offensive in late 2008 with the declared aim of ending cross-border rocket fire that continuously struck southern Israeli towns. Much of the fighting took place in densely populated areas of the small coastal territory. More than 1,400 Palestinians and 13 Israelis were killed.
A report released in 2009 by Goldstone under a mandate of the UN Human Rights Council said both Israel and the Islamist group Hamas were guilty of war crimes.
Israel refused to cooperate with the inquiry and strongly criticized Goldstone's conclusions as biased.
The Israeli group B'Tselem, another group that had filed claims, said the response it received from the military did not detail the findings of the shelling investigation or provide reasons behind the decision to close the file.
"It is unacceptable that no one is found responsible for an action of the army that led to the killing of 21 uninvolved civilians, inside the building they entered under soldiers' orders, even if this was not done deliberately," Yael Stein, B'Tselem's head of research, said in a statement.