“Sudden jihad syndrome”. A bearded savage lives quietly for years, arousing no suspicion, then “suddenly” kills infidels for “no reason.”
Not at all. After their completed missions, background investigations have revealed that all jihadists had a pattern of extremism in conversations with friends and so on. They weren't noticed only because they staged attacks outside of their communities. The MAS personnel in question appear to not have been particularly religious and had any number of non-Muslim friends who vouched for them. Guys with ethnic Chinese and ethnic Indian names - a clear indication of their non-Muslim status, given that Muslims of any ethnic group take up Arabic names upon conversion, which is why Cassius Clay came to be known as Muhammad Ali.