This is just one of an endless string of lies from Israel. Hind Rajab? World Central Kitchen? and many others that we don't know about. They even shot their own hostages waving white flags. Their first reaction is to lie, and if they get caught they say they will investigate. How can anyone believe them anymore, and how can anyone expect their investigation to lead to full accountability and prevention of future incidents? It just baffles me.
Let's not forget the 40 beheaded babies hoax and the mass rape hoax.
Where is the material? "reasonable grounds" is not evidence. I'll just leave this here from the same report[1][2][3]
But the world did see how Palestinian prisoners were raped in prisons.
[1] https://imgur.com/a/TmKGadc
[2] https://imgur.com/a/C6bsMp7
[3] https://imgur.com/a/ADsmgWy
Note the words "corroborated by [...] digital material" (emphasis added).
The quotes in the imgur link do not come up in the report when you use ctrl-f.