British aid worker, a video of whose murder has been released online, had been in Syria for three days when he was seized

After 12 years in the RAF, David Haines decided that he wanted to use his experience to work with NGOs who were operating in some of the world's most turbulent regions. Over the next 15 years, as a security adviser and manager, he worked with refugees in the former Yugoslavia, disabled people in Libya and ceasefire monitors in South Sudan.

He had been in Syria for just three days when he was kidnapped and handed over to Islamic State militants. Along with an Italian aid worker, Federico Motka, and a Syrian driver and translator, Haines had been surveying possible sites for refugee camps that a French charity, Acted, the Agency for Technical Cooperation and Development, was planning to establish, near the Turkish border.

Their translator, who asked not be named, later described the moment the kidnapper struck. "Two very fast cars came up behind – one overtook and the other stayed behind. They shouted at us to get out of the car in formal Arabic. They were wearing black masks and were so professional. They knew that two of us were Syrians and they knew who else was in the car. One of them put a gun to my head and threatened me not to tell anyone what I had seen. They put [Haines and Motka] in the boot of their car and shot out the tyres of our car."

That was in March last year. During that time Haines, 44, has seen a number of other hostages held by the Islamic State released in return for ransoms. Among them was Motka, freed in May this year with the Italian government reportedly handing over almost £5m. Motka later said that he had been tortured, and moved six times. Haines' plight went unreported, however. The UK foreign office advised Haines's family and friends to keep quiet about his ordeal.

Earlier this month, Haines was seen at the end of the video that depicted the murder of American journalist Steven Sotloff, clad in an identical orange jumpsuit. Clutching his collar, Sotloff's killer appeared to threaten that he would be killed if the UK joined military action against Islamic State forces, saying in his distinctive London accent: "We take this opportunity to warn those governments who have entered this evil alliance with America against the Islamic State to back off, and leave our people alone."

Haines's name appeared in a caption on the video, and was immediately reported by media organisations around the world. Even then, members of his family made clear that they were not going to do or say anything that might raise his public profile still further.

Haines was born in east Yorkshire and grew up in Perth in central Scotland, where he attended Perth academy. At 17 he followed his father into the RAF, according to some reports, and served as an aircraft engineer.

He was married twice, and had two daughters: Bethany, aged 17, who lives in Perth, and Athea, aged four, who lives with his Croatian second wife, Dragana, in Sisak, a town south of Zagreb. "He's everything to us," Dragana told the Daily Telegraph. "He's our life. He's a fantastic man and father. Nobody can understand how we are feeling. My daughter keeps asking about him every day.

"She hasn't seen her father for a year and a half. She has gone through so much. She sees me crying all the time. We just don't want to do anything to endanger his life."