It's reactions like that from people like you which allow these idiots to fester in our country and kill innocent civilians.
If he's known to ASIO already, and his brothers got priors for plotting a terror attack, then he should never have been in the country.
With terror related offences, if you get caught, your entire family gets deported. Why take the risk on innocent lives.
It's not that simple. Ask Katrina Dawson what happens when police open fire in a poorly planned operation. If you don't know who she is, she was one of the Martin Place Lindt Siege victims, who was killed when police raided the place (and opened fire with NATO ammunition), which resulted in her being hit and killed by something like 15 bullet fragments, after 20 odd bullets were fired (10 odd into Monis and 10 strays which hit a chair she was behind). * Numbers are rough there.
Before they open fire there are operation guidelines they must follow (including the use of less lethal). So the fact this arsehole is dead and not tasered, no doubt will resulting in wasting money on an inquiry now too.