An air mechanic whose cousin joined the Islamic State terrorist group in Syria is suspected of planting a bomb on a Russian passenger plane that exploded over Egypt’s skies in October, killing all 224 people on board, according to a Reuters report.

Sources familiar with the matter said the EgyptAir mechanic had been detained along with two airport police officers and a baggage handler suspected of assisting in the alleged bomb plot. None of the four have been prosecuted so far, the sources added.

The MetroJet flight crashed in the Sinai Peninsula after taking off from the Red Sea resort city of Sharm el-Sheikh on October 31.

To date, Egypt has publicly said it has found no evidence that the flight was brought down by terrorism, and a senior security official at MetroJet told Reuters that none of its employees had been arrested or were under suspicion. An Egypt Interior Ministry official also said there have been no arrests.

But “after learning that one of its members had a relative that worked at the airport, Islamic State delivered a bomb in a handbag to that person," one of the sources told Reuters, adding the suspect's cousin linked up with ISIS in Syria a year and a half ago.

"He was told to not ask any questions and get the bomb on the plane."

Another source said "two policemen are suspected of playing a role by turning a blind eye to the operation at a security checkpoint. But there is a possibility that they were just not doing their jobs properly."

Egypt says the crash has taken a huge toll on its vital tourism industry, as a government official reported that the country has lost hundreds of millions of dollars.

South Sinai Governor Khaled Fouda was quoted by the state-run Al-Ahram newspaper on Friday as saying that the resort cities of Sharm el-Sheikh and Hurghada are losing more than $250 each month, according to The Associated Press. He added that hotel occupancy in both cities is less than 20 percent.

Russian suspended all of its flights to Egypt after the crash, while Britain has halted flights to Sharm el-Sheikh.