How did Oman, UAE and Israel miss red flags about flydubai co-pilot?

Oman identified flydubai co-pilot's radical leanings before he attempted a 9/11-style attack on flydubai flight but didn't share concerns with other authorities or airlines, WSJ reported. UAE's government-owned Flydubai airline later hired him without contacting Oman to vet his previous employment, while Israel also failed to vet his nationality, as Omani pilots are barred from flying into Israel.