It was just after 6 a.m. on Oct. 7 when the first missiles appeared in the sky, kicking off hours of violence in southern Israel as Hamas militants carried out a terror attack that killed at least 1,200 people.

Rami Shmael —who produced the Supernova music festival, where at least 260 people were massacred on Oct. 7— returned the following day and witnessed its aftermath.

"Outside two cars, there was also two young ladies, naked from the waist down," Shmael said. "One of the victims was gunshot down in the lower part of her body."

Shmael said there was "definitely" a difference between how the bodies of the male and female victims were found.

"What they did to these ladies from the waist down, it's not only rape," Shmael said.

Israeli investigators tell CBS News the priority after the Oct. 7 attack was identifying the victims, so they did not collect evidence of sexual assault. But they say there are eyewitness accounts, photos, interrogation statements and circumstantial evidence pointing to sexual attacks.

In a letter this week, a bipartisan group of 33 U.S. senators urged the United Nations to open an independent investigation into what the senators call "a growing body of evidence" that Hamas committed acts of sexual violence against Israelis.

A supervisor with the Israeli search and recovery team in charge of collecting the bodies showed CBS News some of the injuries he saw and documented, including women whose bodies had lacerations, stabbings and gunshots to their genital area.

The bodies were taken to an Israeli army base that served as a morgue, where Israeli Defense Forces volunteer Shari Mendes says she handled the bodies of female victims.

"Sometimes women were shot in the genitals," Mendes said. "They were shot in the breast. And we saw, a lot of women came in, sometimes just in underwear. The underwear was very bloody."

An IDF medic who did not want to be identified described to CBS News what he says he found in one kibbutz.

"The one on the floor, her legs are wide open," the medic said. "And she was shot at the back side of her head, and her pants are pulled down and there's a pile of semen on the lower part of her back."

In a statement to CBS News, Hamas said "we categorically reject false allegations of rape," calling the allegations "misleading propaganda."

Other militant groups and criminal organizations also took part in the attack, U.S. officials said.

Israeli investigators say most of the victims of sexual violence on Oct. 7 did not survive to tell their stories.

"I think every one of those cases struck me as just being a terrible message of hatred," Mendes said. 

In:
• Hamas
• Israel
• Sexual Assault