the large quantity of homes destroyed, and collateral damage from home demolitions, it became an increasingly controversial tactic. Families began providing timely information to Israeli forces regarding suicide bombing activities in order to prevent the demolition of their homes, although families doing so risked being executed or otherwise punished for collaboration, either by the Palestinian Authority or extrajudicially by Palestinian militants. The IDF committee studying the issue recommended ending the practice because the policy was not effective enough to justify its costs to Israel's image internationally and the backlash it created among Palestinians. With complete ground and air superiority, mass arrests were regularly conducted by Israeli military and police forces; at any given time, there were about 6,000 Palestinian prisoners detained in Israeli prisons, about half of them held temporarily without a final indictment, in accordance with Israeli law. The tactic of military "curfew" – long-term lockdown of civilian areas – was used extensively by Israel throughout the Intifada. The longest curfew was in Nablus, which was kept under curfew for over 100 consecutive days, with generally under two hours per day allowed for people to get food or conduct other business. Security checkpoints and roadblocks were erected inside and between Palestinian cities, subjecting all people and vehicles to security inspection for free passage. Israel defended those checkpoints as being necessary to stop militants and limit the ability to move weapons around. However some Palestinian, Israeli and International observers and organizations have criticized the checkpoints as excessive, humiliating, and a major cause of the humanitarian situation in the Occupied Territories. Transit could be delayed by several hours, depending on the security situation in Israel. Sniper towers were used extensively in the Gaza Strip before the Israeli pullout. The Israeli intelligence services Shin Bet and Mossad penetrated Palestinian militant organizations by relying on moles and sources within armed groups, tapping communication lines, and aerial reconnaissance. The intelligence gathered allowed the IDF, Israel Border Police, and Israel Police, including Yamam and Mistaravim special forces units, to thwart hundreds of planned suicide bombings. The intelligence gathered also helped create a list of Palestinians marked for targeted killings. Israel extensively used targeted killings, the assassinations of Palestinians involved in organizing attacks against Israelis, to eliminate imminent threats and to deter others from following suit, relying primarily on airstrikes and covert operations to carry them out. The strategy of targeted killings had been proposed by