Unsurprisingly, the family of Mahmoud al-Mabhouh are convinced that his death was the work of Israel. His older brother, Hussein, said the assassinated Hamas commander had owned a sewing factory in Damascus, but lived a "shadowy and secretive life" in Syria. "Each time he called us he talked from a different phone."

Hussein – a Hamas activist and head of a Gaza charity – said this was the fourth attempt on his brother's life. "Regardless of the evidence, it is in the interests of the Mossad to assassinate him," he told The Independent.

Mabhouh was nearing his 50th birthday when he was killed. Born on Valentine's Day in 1960, he was an early member of Hamas's military wing, but he was not one of the movement's high-profile figures and was not particularly well known in his native Gaza, which he left in 1989 after his involvement in the killing of two Israeli soldiers.

Sgt Avi Sasportas was abducted outside the coastal city of Ashkelon, near the Gaza Strip, and shot dead. The body of Cpl Ilan Saadon who was seized the same year while hitchhiking just north of Gaza, was found in 1996 buried under a road south of Tel Aviv.

According to Hamas, Mabhouh went into hiding for two months after escaping a raid in which Israeli forces dropped on to his roof while other troops dressed as farmworkers raided his garage. He crossed the border into Egypt and reached Syria by way of Libya.

But according to Israeli officials, Mabhouh had been instrumental in importing weapons into Gaza from Iran at the time of his assassination. Yesterday, Eitan Haber, who was a chief aide to Prime Minister Yitzhak Rabin in the 1990s, said Mabhouh was known and wanted "for years". "He was a VIP in Hamas's terror organisation," he said, declining to elaborate.

Hamas would say only that Mabhouh played "a continuous role in supporting his brothers in the resistance inside the occupied homeland".

Born in the Jabalya refugee camp, one of 14 children, Mabhouh was a secondary school drop-out who was apprenticed as a car mechanic and eventually opened a garage. He was a keen body-builder in his youth and won a weight-lifting competition.

After joining the Muslim Brotherhood in 1978, he met Sheikh Ahmed Yassin, who went on to become the founder and Gaza leader of Hamas before being assassinated by an Israeli strike in 2004. Mahmoud had been among Brotherhood groups questioning the-then relatively pacific role of the movement. He joined its first underground cell and after being imprisoned for possession of an AK-47, he became a founder member of Hamas in the year the first Intifada erupted in his own neighbourhood of Jabalya in 1987. He was married with four children.

According to his niece, Hiba, an attempt was made to capture Mabhouh in Beirut in 1999. His Egyptian and Sudanese would-be captors had intended spiriting him away by boat, but he escaped. She described the assassination of her uncle as a "Hollywood production but it didn't have the happy end of a Hollywood movie". She said the international row over the operation was "a big blow to Mossad. This is not the end they wanted."