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 by Shin Bet to carry them out. The strategy of targeted killings had been proposed by Shin Bet, which determined that while it was impossible to stop every single suicide bomber, suicide bombings could be stopped by directly attacking the conspiratorial infrastructure behind them by killing operational commanders, recruiters, couriers, weapons procurers, maintainers of safehouses, and smugglers of money which financed the bombings. Israel was criticized for the use of helicopter gunships in urban assassinations, which often resulted in civilian casualties. Israel criticized what it described as a practice of militant leaders hiding among civilians in densely populated areas, thus turning them into unwitting human shields. Throughout the Intifada, the Palestinian leadership suffered heavy losses through targeted killings.