Palestinian Musa Abu Jarrad shrugs off any notion of reconciling with the Hamas group he blames for the death of his son, a Fatah member, in 2007 factional fighting in Gaza.
"The angel Gabriel himself couldn't make me reconcile with my boy's killers," the 70-year-old says, anger shaking his slender frame.
Abu Jarrad lost his son Bahaa, 36, in fighting that erupted between members of the rival political groups a year after Hamas won a surprise electoral victory.
His anger and wish for revenge is shared by many grieving families, even as Hamas and Fatah seek to implement a unity deal.
Any reconciliation "will be stained with blood and will not last unless we avenge the deaths of our sons," Abu Jarrad warns.
"Hamas ambushed my son and killed him in cold blood and now they want to reconcile me with those who killed him? How is that possible?"
Hamas and Fatah have long been political rivals, but tensions spilled over into violence in 2007 with Hamas forces eventually routing their Fatah rivals and taking control of the Gaza Strip.
In all, 346 people were killed in fighting in the Gaza Strip in 2007, says the Palestinian Independent Commission for Human Rights.
After years of bitter division, the two sides inked a surprise unity deal in Cairo in May, committing to the formation of a transitional government and elections within a year.
But for Abu Jarrad, there can be no reconciliation.
"They will not fool us," he warned. "I will never accept any kind of money as compensation, all I want from the next government is retribution."
Bahaa's widow, left to fend for four children, agrees with her father-in-law.
"We just want retribution. If the reconciliation doesn't give us that, then we don't want it."
The desire for revenge is equally strong among the families of Hamas members killed in the internecine fighting.
"Punishment is the most important thing because those who killed my husband are not entitled to live a normal life anymore and should pay for what they have done," says Mona al-Rifati, who lost her husband, Hamas sheikh Mohamed al-Rifati.
As she speaks, her 19-year-old son Hamza interrupts.
"I will not back down for the sake of reconciliation. We were victims in the Fatah-Hamas conflict, we will not become victims of their reconciliation."
A court in Hamas-run Gaza sentenced three men accused of Rifati's killing to death last year, but his family fears the sentences will not be carried out because of the reconciliation efforts.
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Their fears may not be unfounded.
"These files are now the responsibility of the social reconciliation committee," a body that has yet to be formed under the unity deal, says Hamas spokesman Taher al-Nunu.
"If the committee ratifies the sentences, they will be implemented, but if it doesn't, they won't."
Hamza al-Rifati is clear about the desired fate of his father's killers.
"If I see the person who committed the crime walking down the street, I will not stand still and watch him breathe, I will take my revenge. No one can see their father's killer free."
Hassan Ziadeh, a psychological expert at the Gaza Community Mental Health Programme, said the factional fighting created a "dysfunction" in Gaza's society.
"Feelings of anger, hatred and revenge are a normal reaction," he said.
"It will not be easy for some families to forgive, and for some it will be, culturally speaking, hard to accept and live with it."
Umm Ahmed is one of those who cannot forgive the deaths of her husband and brother-in-law, both Fatah members.
"How can I prevent my son from taking his father's revenge after he was killed in front of him in our house," she shouts, her large frame vibrating with rage.
Her 19-year-old son, sitting by her side, displays a picture of his father's dead body which he uses as a cellphone screensaver "to always remind me of what Hamas did to him".
Another mother and a similar story echo in the home of Umm Ali. Her two sons, both members of the Fatah-dominated Palestinian Authority security forces, were killed by Hamas fighters. She lost two other sons in fighting with Israeli troops.
"The occupation killed Yusef and Mohamed, and Hamas killed Hadibi and Ibrahim!" she screeches.
There can be "no reconciliation after they took away my sons, only punishment, and they must be killed just as they killed our children," says Umm Ali.
Nunu urges a more measured approach, and pledges that a committee "will discuss each and every case in detail and find a way to please every family."
It would be a mistake for families to revert to vigilante justice, he warns.
"These are not family issues because the killings were motivated by politics only."
Ibrahim Abu al-Naja, a Fatah official in Gaza, says both sides have agreed to ensure that the families of those killed in the factional fighting will "be compensated without knowing the killers' identities."
"The factions who were behind those killings ... must resolve these problems with the families," he said.
"We want the law to be implemented so that no one takes matters into their own hands."