Probably by crucifying them, as Hamas recently declared that it will crucify all "traitors." After all, Koran 5:33 states: "The punishment of those who wage war against Allah and His messenger and strive to make mischief in the land is only this, that they should be murdered or crucified..."
"Hamas Executes Gaza Residents for Helping Israel," by Hana Levi Julian for Israel National News, January 7:
(IsraelNN.com) The Hamas terrorist organization has reportedly executed several Gaza residents accused of passing information to Israel. The victims were accused of helping the IAF conduct air strikes and IDF ground forces carry out assassinations in Gaza.
Among those killed were three brothers, all of whom were executed in public. A fourth brother was murdered by Hamas supporters earlier in the week after they escaped a prison run by the guerrilla group.
A total of six Gaza residents were executed by Hamas since last week, all of whom were accused of being collaborators...