Israel’s denial of fair trials to prisoners may also constitute war crimes, the group stated.
Addameer had been collecting evidence on Israel’s use of torture and ill-treatment against Palestinian detainees since late August.
Prison officers were found to have ill-treated some 50 detainees, studied by the prisoners rights group, of whom about half were subjected to torture.
Detainees included women, university students, union workers, human rights defenders and Palestinians lawmakers.
An Israeli court in Jerusalem issued a gag order on 10 September that barred Addameer and the general public from publishing information on cases of Palestinians being held at the Russian Compound, a notorious Israeli detention center in Jerusalem.
The court renewed the order twice after that, until it expired on 7 December.
“Since its creation, the occupying state developed and enforced laws and practices that led to both: the systematic use of torture and to absolute impunity for the perpetrator of this crime,” Addameer writes in a report that goes into some detail about the forms of torture Israeli prison officers employ.
These include beatings, sleep deprivation, stress positions, sexual harassment and others.
More than 70 Palestinians have died after torture in Israeli custody since 1967, according to Addameer’s research.
This number includes 23 prisoners who died after Israel ratified the United Nations convention against torture in October 1991.
Still, not a single individual or entity was ever held accountable.
Overall, some 220 Palestinians have died in Israeli custody since 1967.
Israeli officers “hit, slapped, punched, poked (using their fingers), and kicked the detainees,” in some cases causing them life-threatening injuries.
To make matters worse, officers sometimes blindfolded detainees “so they would not expect the beating or know where it is coming from,” according to the report.
Beatings would sometimes last dozens of hours and be done by more than five different officers at once.
The complicity of Israeli doctors in crimes of torture is not to be ignored, Addameer stressed.
In some cases, Israeli doctors faked medical assessments of detainees, qualifying them for further interrogation despite there being clear signs of torture on their bodies.
To maximize pain and pressure, Israeli officers would sometimes force detainees into stress positions before beating them.
Stress positions not only impose physical pain on detainees, but are means of applying psychological pressure as well.
In almost all stress positions, Addameer says, detainees are forced to maintain a position designed to make them lose balance, giving cause to Israeli officers to beat them.
One such position has the detainee’s legs cuffed to the legs of the chair and the hands to the other side, forcing their back to arch over the seat of the chair.
Interrogators can then either sit on or beat the detainee’s abdomen.’
Read more: How Israel tortures Palestinians