By Alan Johnston
BBC News correspondent in Gaza
The Palestinian militant movement Hamas says it has killed a man it suspected of collaborating with the Israelis.
Hamas has said it will hunt down other informers
Hamas said he was linked to the death of its spiritual leader, Sheikh Ahmed Yassin, who was killed in an Israeli missile strike in March 2004.
The suspected informer's body was found in a street in Gaza. The man, who was in his 20s, had been shot many times.
The militant Islamic group has warned that it will take action against other suspected informers.
Hamas said the man had supplied the Israelis with information as they prepared to assassinate Sheikh Ahmed Yassin, the founder of Hamas and its spiritual mentor.
His death was a devastating blow to the movement.
But Sheikh Ahmed Yassin's assassination was just one in a long series of Israeli killings that has devastated the organisation's upper ranks.
Hamas men often die in very accurate missile strikes, frequently launched from unmanned spy planes.
There is much speculation in Gaza as to how the Israelis are able to target these high-ranking figures with such apparent ease.
It is often thought that they are assisted by informers.
In the nearly 40 years that they have occupied Gaza, the Israelis are widely believed to have built up an extensive network of collaborators.
Hamas says it knows the identity of several more suspected informers and it has warned that they will be hunted down.
Israel justifies its targeting of militant leaders by saying that they prevent attacks on Israeli civilian and military targets.
However, human rights groups describe the killings as extra-judicial killings.