Professionals missed opportunities to prevent two teenage British Muslims being radicalised before they were killed after travelling to fight in Syria, a serious case review has found.
There was "no recognition" that Abdullah Deghayes, 18, his 17-year-old brother Jaffar and their three siblings were becoming vulnerable to radicalisation in Brighton.
There was also little understanding of the part religion played in the lives of Abdullah and Jaffar who were believed to have been with the al Qaida-affiliated Al-Nusra Front when they died, the review added.
A third brother Amer Deghayes, a former finance student, also travelled to Syria in a bid to overthrow dictator Bashar Assad's government.
He told ITV News in 2014 that he was prepared to suffer the same fate as his brothers, saying he had promised Allah he would continue on the path of jihad "until I get killed".
Missed opportunities to intervene in the siblings' lives were highlighted in the report following the deaths in 2014 of Abdullah and Jaffar, who were referred to as W and X.
In 2013, concern was raised by a school that some young people were converting to Islam and some had been paid by a relative of the brothers to attend a gym behind a place of worship.
The report said no further information was obtained about the activities at the gym.
The second opportunity came in the same year after Jaffar was referred to a panel following an "emotional" comment he made about Americans. But the panel concluded Jaffar was "not at risk of being drawn into terror-related activities".
The report said: "Both these instances were missed opportunities to learn more about the activities of the young people and to understand the links between young people in Brighton."
It added: "Moreover at that time there was little local or national knowledge or understanding of the risks to children from being exploited into radicalisation to go and fight in wars elsewhere in the world."
The report pointed to the family being targeted directly in Brighton. The Deghayes brothers are the nephews of Omar Deghayes, who was held by the United States at Guantanamo Bay between 2002 and 2007 after he was arrested in Pakistan.
Anti-Islamic graffiti was reported in the area in Brighton where the brothers lived from 2007 onwards, including a 12-inch high daubing stating "Behead all Muslims" in 2009.
The report also revealed that:
:: The five siblings' father made them get up at 4.30am to study the Koran and punished them if he felt they were not studying properly, including whipping them with electrical wire
:: Following his arrest in 2012, Jaffar shouted at officers that they "would die as they did not follow Allah, that they would burn in hell on judgment day"
:: The report's authors said they were unable to point to how the brothers were radicalised
:: News that Jaffar and Abdullah had gone to Syria came as a "total surprise and shock" to professionals
:: There was no recognition that the siblings were vulnerable to radicalisation or prepared to fight in a conflict abroad