$1b pricetag to monitor terror suspects
ASIO would need its annual funding to be boosted by $1 billion to watch all potential terror suspects.
Experts say the national security agency would need around 9000 security employees to do the job - a far cry from the 1850 currently employed in total.
It would take up to 10 officers to watch a suspect properly over an eight-hour shift, Fairfax Media reports.
If the suspect was to have round-the-clock access, that would require 30 officers over a 24-hour period.
ASIO currently has 400 potential terror cases, which would mean 12,000 officers for counter-terrorism surveillance alone.
Over the weekend, authorities revealed Bourke St terrorist Hassan Khalif Shire Ali had his passport revoked in 2015 over fears he was trying to travel to Syria to fight for Islamic State.
About 240 Australians have had their passports cancelled on the advice of ASIO to the foreign minister.
But Ali was not classified as a high-risk terror threat, and authorities said he was not being actively monitored prior to the Friday attack.
Mohammed Omran, spiritual leader of the Hume Islamic Youth Centre which Shire Ali attended, has questioned what authorities did to stop the attacker, who had been known to federal police.
"This person was on the watch list. So what did they do? Nothing," Omran told The Australian today.
"This bloody prime minister, instead of turning the heat on somebody else, he should answer us about what he did.
"He has spent billions of dollars - billions - on security service. And what is the end result? We have crazy people in the street."
According to ASIO, there is no official "terror watch list".
"ASIO does not maintain a 'terror watch list'," a statement from the organisation to news.com.au read.
Anyone deemed to be a risk to national security can be investigated by ASIO or the Joint Counter Terrorism Team, which the agency is part of, along with state and Federal Police (AFP).
Instead of monitoring all persons thought to be capable of carrying out an attack, ASIO cherrypicks who to watch closely based on "a range of prioritisation systems and review mechanisms".
Prime Minister Scott Morrison on Monday urged imams to watch out for "infiltrators" and "shady characters" in mosques who preyed on vulnerable young men, and said imams "can't look the other way".
- with Megan Palin and wires