By Matthew Champion and Ian Dunt
There is still time for Hamas to "pull back from the brink" and halt its slide into an organisation that rules purely through terror, aid workers have said.
"Incontrovertible" evidence released this week linked Hamas militia to the torture of scores of men and the murder of at least two dozen labelled as collaborators during the Israeli military offensive.
According to Amnesty International UK, during the Israeli bombing that killed 1,300 Palestinians at the end of December and start of January, Hamas gunmen were guilty of kneecappings, punishment beatings and killings to people linked to the Palestinian Authority and its president Mahmoud Abbas' Fatah faction.
"Four masked men came to my house on December 31st 2008 at about 16:00; they were armed with Kalashnikovs," one victim told Amnesty International UK.
"They took me behind my house; they did not say anything. They shot me in the back of my right knee and then shot my left leg three times. My relative tried to intervene but they threatened to shoot him too."
According to a report many of the dead were shot while recovering in hospital.
British politicians who opposed Israel's military adventure said the onslaught inevitably weakened the position of the more moderate Fatah faction.
"They made it possible for Fatah to be undermined," Martin Linton, chair of Labour Friends of Palestine, told politics.co.uk.
"In the realm of psychology there's a well known inclination for people under attack to rally under whoever is in charge.
"I'm not saying whether that's the right or wrong thing to do. But because of this natural human reaction the attack acted as a recruiting serjeant for Hamas - at least for a period."
The report's author, Donatella Rovera, who led a team of Amnesty researchers into Gaza during the bombing, said the evidence was damning.
"My colleagues saw a vast number of victims and met with the families of people who have been killed," she told inthenews.co.uk.
Ms Rovera said she had seen people herself with broken bones, gunshot wounds to the legs, dead bodies and medical certificates.
"The pattern has been fairly uniform. Armed guys, often masked, turn up at people's homes brandishing weapons in a blasé fashion," she said.
"Usually they do not keep the people they take for very long, sometimes holding them next to the house or taking them away to a nearby location.
"The next the family hears is a call from the morgue to collect the body."
Many of the victims were detainees from a prison partially destroyed by Israeli bombing at the start of the offensive. But within 24 hours most had been rounded up and either tortured or killed.
But Ms Rovera, head of research for Amnesty for Israel and the occupied Palestinian territories, said it was unclear how far up the chain of command the violence went.
"Whether Hamas ordered it or not is a different matter - the armed militias are running wild and the political leadership does not have the will or ability to actually rein them in."
In one of the few Hamas responses to the allegations, spokesman Taher al-Nunu denied the charges, dismissing them as "lies spread by Ramallah".
Ms Rovera told inthenews.co.uk that she had been due to hold talks with Hamas officials to discuss the allegations contained in the report, but that the discussions had been called off due to ongoing intermittent rocket-fire between Gaza and Israel.
"One can only speculate as to what the reasons are," she said in response to questions whether Hamas was trying to eliminate its political opposition in Gaza.
But Ms Rovera insisted calls for an independent, impartial and non-partisan national commission to investigate the allegations were "totally feasible".
"People are not scared of Hamas in Gaza; Hamas relies on the support of the local population," she said.
"It is still possible to put pressure on the Hamas leadership, who were elected through the ballot box and still enjoy a lot of support [because] they are quite keen to keep it that way.
"The alternative is to transform into a group that imposes its authority purely by terror.
"One pressure that is not available is pressure from the west. No engagement consequently means no leverage."
The allegations against Hamas come as Israelis go to the polls to elect a new parliament.
Either Likud leader Benjamin Netanyahu or Kadima chairman Tzipi Livni is expected to be asked to form a coalition government later this week.