The father of an aviation engineer on board the missing Malaysia Airlines plane has vehemently defended his son, who is being investigated because his training may have equipped him with the technical knowledge and skill to control the jetliner. Investigators were examining Mohd Khairul Amri Selamat, the Malaysian engineer, and crew members aboard flight MH370 as police renewed theories that the plane could have been hijacked, officials said. The engineer's father, Selamat bin Omar, said his son did not have the technical knowledge to divert the aircraft from its set course from Kuala Lumpur to Beijing. Malaysian authorities said that someone with substantial knowledge of aviation navigation diverted the plane from its original path on March 8. The search area now spans from Kazakhstan to the south of the Indian Ocean. "I can't change what other people think of my son, but I am 100 per cent sure he was not responsible," said Selamat, 60. "He repaired plane engines, he doesn't know how to change the route." Watch: Visitors write messages for passengers of missing MH370 Selamat said his "good son" had excelled at school, cared for his family, and had friends of many races. He had a wife and 15-month-old baby at home in Shah Alam, and was a soccer fanatic. Investigators are scrutinising the background of each of the 239 people on board MH370. Khairul identified himself as an employee of Swiss-based ExecuJet Aviation Group in a photograph posted on social media in 2011. Graeme Duckworth, the Asia managing director for ExecuJet, said the 29-year-old had been an aircraft engineer at the company for more than three years. "Without question, he was one of our better engineers, but he specialised in business jets, not commercial jets," he said. Duckworth said Khairul was travelling to Beijing to service a Learjet when the plane vanished. Hishammuddin Hussein, Malaysia's acting transport minister, said passengers, crew and ground staff were being investigated, but everyone was innocent until proven otherwise. "For the sake of their families, I ask that we refrain from any unnecessary speculation that might make an already difficult time even harder," Hishammuddin said yesterday. Selamat said that police had not contacted him or any member of Khairul's family. "If they do, I'll be ready. I have nothing to hide," Selamat said. "I just hope he will be found soon."