By 5am, the helicopters were waiting

It was just before dawn yesterday when the Middle East was turned upside-down. Sheikh Ahmed Yassin had emerged from a hiding place: the whereabouts of which was one of Gaza's best-kept secrets. It was a moment Israel's government had waited for. Six days ago, it took the decision to assassinate the founder of Hamas. But for six days, the Israeli military could not find him, so good were his security precautions.

But yesterday, Sheikh Yassin decided to attend dawn prayers at Mujmaa Islami mosque, which he had founded, in the Sabra neighbourhood of Gaza City where he lived. It was a fatal mistake. At 4.30am, Israeli intelligence learnt that the wheelchair-bound paraplegic was on his way to the mosque. The precious information was passed to Shaul Mofaz, the Israeli Defence Minister. He reported it to Ariel Sharon, Israel's Prime Minister.

Sheikh Yassin was chatting with his supporters in the mosque about prayer times, which had just changed at the beginning of a new Muslim month, seconds before the missile struck. Fittingly, it was Safr, regarded as the month of disaster, in the pre-Islamic Arab calendar.

Bassam Sharnobi, 25, one of Sheikh Yassin's neighbours at his family home near the mosque, said: "Sheikh Yassin leafed through the new prayer times ... A Palestinian UN employee came over and told Yassin that there were helicopters hovering in the sky. This was at about 5am."

Israeli helicopters overhead would have been an ominous sign for Sheikh Yassin, a man Zeev Boim, an Israeli cabinet minister, had said was "marked for death". According to Mr Sharnobi, Sheikh Yassin responded: "God is the protector. Those who fear God will be helped and protected." Mr Sharnobi continued: "Yassin was with four or five of his bodyguards. His two sons were praying too. Some kids pushed and shoved at each other to offer to help Yassin in his wheelchair. After he had gone a few yards, three missiles were fired. One of them hit his wheelchair. It was pinpoint shooting." It killed Yassin, wounded his sons and killed at least six others.

The Israeli government had decided some time ago to kill Sheikh Yassin, but push came to shove after a twin suicide bombing in the port of Ashdod, which killed 10 Israelis on 14 March. Israel has faced plenty of suicide bombings before, many with far higher death tolls. But this was different. This time, the bombers had penetrated the security of Israel's main port. It was a sign that the militants could strike even some of Israel's best-guarded sites. The Israeli security establishment decided it needed a response.

The day after the suicide bombing, Mr Mofaz returned from a US trip and called for a meeting of top advisers. Military intelligence gave an assessment that Hamas had taken a strategic decision to escalate its attacks against Israel. On Tuesday 16 March, senior security officials decided their response would be a "dramatic operation". That meant assassinating Sheikh Yassin. At every stage in the operation, which involved Israeli intelligence tracking the Hamas spiritual leader, the decision was referred to Mr Sharon for his personal approval and he gave the final go-ahead yesterday morning. But ministers from Mr Sharon's coalition partners in the Shinui party voted against the decision, and spoke out against it.

Mr Sharon recently proposed an intention to "disengage" from Gaza and possibly some settlements in the West Bank but some viewed this as a shrouded attempt to appeal to moderates in the Likud party. Yesterday's assassination could also be seen as an effort to please the Likud right.

Sheikh Yassin had previously been attacked on 6 September, when an Israeli helicopter fired missiles at a building where he and other Hamas leaders were hiding. Yassin was slightly wounded in that attack. Hamas activists said he had stopped sleeping at his home after that, and minimised the time he spent there during the day. In October, when there was talk of a ceasefire, he reduced his security measures. But in February, after an Israeli official said he was "marked for death", Sheikh Yassin started taking new precautions.

After Yassin was buried in Sheikh Redwan cemetery yesterday, a new Hamas leadership was appointed.