Israeli soldiers executed at least 19 civilians in Gaza City in December, witnesses said, describing how women and girls were separated from their families, beaten and subjected to strip searches.

Human rights groups have collected testimonies about the alleged mass executions, and Al Jazeera has obtained footage and testimonies from members of a family about the Dec. 19 attack.

“Tanks and bulldozers surrounded the building. Shells had been hitting the building for days. The situation was desperate,” said Umm Odai Salem, whose husband was among those killed.

The Israeli soldiers stormed the building. “They knocked on our door. My husband…told them we were all civilians. They took him to another apartment. I followed them and begged them to let him go because we were civilians,” she said.

“They beat me and my daughters. They put us women in one place and threatened us with guns and knives. They forced us to take off our clothes. They searched us and insulted us with the most terrible words,” Salem added.

The soldiers ignored their pleas and “executed” all the men they had rounded up outside.

“My husband was one of the 19 men killed in that building. They ordered them to submit and executed them. They killed them all.”

“She was dying”

The footage shows the bodies of men with bullet holes in their backs.

After the men were killed, the apartment where Salem and her daughters were taking refuge was attacked, one of her daughters told Al Jazeera, killing her three-year-old sister Nada.

“I held my sister in my arms. Then the shelling continued. Nada was hit. She made a few quiet noises. She asked for some water.”

“I thought she was crying. But she was dying. Splinters had penetrated her head, eyes and neck. My sister tried to carry her body, but she fell out of her arms at the door.”

William Schabas, a professor of international law at Middlesex University in London, says the footage, along with witness statements, would constitute evidence International Criminal Court.

“I should add that it’s not really important to show that they are civilians. Mass executions of even fighters, even combatants, are a war crime,” he told Al Jazeera.

Schabas, who was chairman of the investigative commission Gaza war 2014added that in addition to witness statements and corpse photographs, prosecutors would also have to provide the identity of the perpetrators in order to even bring the matter to trial.

“That is one of the big challenges in a situation like this, [which] “Really it’s about finding out who the people were who fired the weapons or gave the orders,” he said.

“Systematic” murders

Muhammad Shehada, of the Euro-Mediterranean Human Rights Monitor in Copenhagen, told Al Jazeera his organization believes there is a pattern of “systematic” killing takes place on the ground.

“In at least 13 executions on site, we have confirmed that they were arbitrary on the part of the Israel Defense Forces,” said Shehada, the group’s program and communications chief.

Members of the monitoring group, who visited crime scenes and collected statements from witnesses and family members of those killed, as well as reports from the Ministry of Health in Gaza, said the soldiers had a sense of impunity.

Israeli forces have already been accused of executing civilians since the current conflict broke out on October 7th.

In December, the United Nations human rights office, citing a case, called for an independent investigation into allegations that Israeli soldiers executed at least 11 Palestinian men in Gaza, which it called a “possible war crime.”

The key question is how such investigations would be carried out, analysts say, since none of the facilities that could investigate alleged Israeli crimes against Palestinians are currently allowed into the Gaza Strip.

Many Palestinians have also blamed the Israeli forces Mistreatment and torture after being held in Israeli prisons.

On Friday, Muhammad Abu Samra, a detainee released in Gaza, accused the Israeli army of “torture” and “beatings.”

“The army…threatened to shoot us while we lay naked in the cold. Then female soldiers attacked us and we were subjected to obscene insults,” Abu Samra told Al Jazeera.

Another released prisoner, Abdel Qader Fatesh, said soldiers ordered him to remove his clothes, tied his hands and blindfolded him.

A UN human rights official said this on Friday Prisoners in the Gaza Strip were detained for weeks in unknown locations and physically abused.