The reports speak of wanton killings of civilians, including an elderly woman and a mother and her children, as well as the unnecessary destruction of buildings.
Yehuda Shaul is a former soldier and co-founder of Breaking the Silence. The group advocates moral behavior by Israel's military, the IDF.
He is collecting testimony from soldiers who fought recently in the Gaza Strip. He says some of them told him their units were not advised to spare civilians.
"Being careful not to hurt civilians wasn't even said. I'm not saying that all units, all the time, all over. But at least, five-six different battalions that we've heard from, commanders in the briefings before the operations didn't even mention the possibility of bumping into innocent victims in the area," he said.
The Israeli military's Advocate General in Tel Aviv ordered an investigation into the cases leaked to the media. But the Advocate General closed those cases recently, saying the allegations were based on hearsay - not firsthand accounts.
Major Yehoshua Gertler, a military lawyer with the unit that is investigating the cases, tells VOA more investigations are under way.
"As part of this investigation, two other incidents surfaced which were also investigated as part of the same investigation, but it focused on particular incidents and not on more general claims which are being investigated on other levels and by other organizations within the IDF," said Gertler.
Some soldiers have come forth to denounce what they say was a permissive attitude toward civilians.
Some who say they witnessed wrongdoing are conscripts who wish to remain anonymous.
In a recording provided by Yehuda Shaul's group, one soldier says that during preparations for the Gaza assault, a rabbi brought in by the army gave him and his comrades spiritual guidance that - to him - sounded like license to kill Palestinians indiscriminately.
He said the rabbi told him and his comrades that the battle in Gaza was the battle of the sons of light against the sons of darkness, of total good against total evil.
In response, an Israel Defense Forces official told VOA there were a number of incidents where - in his words - rabbis went too far in briefings and materials
distributed to soldiers and they have been reprimanded.
Palestinian officials say Israel's assault on Gaza killed more than 1,400 people. The assault was retaliation for Hamas rockets fired from Gaza at Israeli communities and it had wide support among Israelis.
Some Israelis say allegations of excessive force are being used by leftists to discredit the IDF.
Yehuda Shaul says he continues to interview soldiers. His group plans to issue a report in a few months.
"Until today, we've interviewed 16 people, and I can say very much the stuff that we hear from soldiers who served in Gaza are very much in line with the accounts that were published a week ago in the Israeli media," he said.
Israel's military says that if atrocities did occur, they were exceptions.
Several soldiers have come forward in support of the military's position. One is Sergeant Major Jeff Gafni, a 65-year-old reservist who has fought in every one of Israel's conflicts since the 1967 Arab-Israeli war. He was in combat in the Gaza strip and says the moral training soldiers received guides them to protect civilian bystanders. In the guerrilla warfare of Gaza where Israel says Hamas was using civilians as human shields, that guidance posed a challenge, he says.
"...I do understand that as a body built of so many individuals, there might be a case of somebody stepping out of line. But that's called stepping out of line. That's not the norm," he said.
Israeli human rights groups, meanwhile, are calling for an independent body to investigate the claims. That is the only way, they say, to discover the truth.