The ISIS militant who appears in a video purporting to show a boy executing an captive Israeli-Arab is a French terrorist whose relatives include a notorious Islamist who slaughtered Jewish children and a woman who took her baby to join the violent extremists. Sabri Essid has been identified as a well-known jihadist, and the half-brother of Mohammed Merah, who shot dead three children, a rabbi and three paratroopers during a terror rampage in the French city of Toulouse. But the two, who are understood to have been close before Merah's 30-hour stand-off with French special forces ended in his death, are among a number of extremists radicalised within the same family. Merah's sister Souad is known to have travelled to Iraq and Syria to join Islamic State with her four children - including her nine-month-old baby. Family: The man on the right of ISIS's latest horrific video has been identified as Sabri Essid, a French terrorist who is a member of a family with a number of radicalised extremists . Essid, a married father, was named by security experts earlier today, after he appeared alongside the young boy in a video claiming to show the execution of a so-called Arab Israeli spy. The man  believed to be Essid stands by the boy speaks in French as he refers to the attack on a kosher supermarket in Paris in January in which four Jews were killed. 'Oh Jews, indeed Allah has gifted us with killing your followers in your own stronghold in France,' says the man. However, doubt has been cast on the authenticity of the video, which is heavily edited. Experts have questioned whether the boy, thought to be about ten, was really the person who pulled the trigger, supposedly murdering 19-year-old Muhammad Said Ismail Musallam with a single gunshot. There is less mystery surrounding Essid himself, who has long been known to counter-terrorism forces. 'The similarities between Essid and the man in the video are very clear,' said an investigating source in Paris. 'Plenty of experts have made the link.' Terrorist: Mohammed Merah, Essid's half-brother, killed seven people - including three children - in 2013 . Shooting: The 23-year-old targeted the Ozar Hatorah Jewish school in Toulouse, also killing a rabbi . A French police source has also told AFP, France's national news agency, that 'we are checking' the identity of the man in the video. Essid, 30, from Toulouse, was caught in Syria in December 2006 in a house known to shelter Al-Qaeda members on their way to Iraq. He was sent back to France and was sentenced in 2009 to five years in jail, including one year suspended, in a case involving an Iraqi jihadist network. On his release in 2010, he returned to Toulouse - where he became a constant companion of half-brother  Merah. His father had lived with Merah's mother, and Essid was close to the killer and his brother Abdelkader. Merah, 23, would go on to wreak terror in the town, shooting three soldiers, a rabbi and three school children outside a Jewish school, before being shot dead. Radicalised: Mohammed's sister Souad Merah, pictured, took her four children to join ISIS last year . Horror: The family of Muhammad Musalam, 19, purportedly shot in the ISIS video by the unnamed child, have said the Arab-Israeli was not a spy. Pictured: Parents Said and Hind Musalam mourn in the family home . Essid left France for Syria in 2014, as did Souad Merah, the sister of the Toulouse gunman, who took her children on the bus south from Toulouse to Barcelona, where they boarded Turkish Airlines flights to first Istanbul and then Gaziantep. Her husband Abdelouahed El Baghdadi, was arrested by French authorities, in September last year when he arrived back at Toulouse airport with the two older children. Their mother Souad Merah is believed to be in Algeria with the two youngest children. But it is not clear if Essid's wife and children travelled with him to Syria.
Sabri Essid, a French citizen, has been identified as man in the lSIS video . Essid, a married father, thought to have joined Islamic State last year . The 30-year-old has served time in France for terror-related offences . Essid part of a family of extremists, including Toulouse terrorist . Half-brother Mohammed Merah killed a rabbi and three children in 2013 . Shot dead by French special forces after 30 hour siege in apartment . Merah's sister Souad travelled to Syria last year with her four children .