A deadly terror attack at Sydney's Bondi Beach is feeding speculation of potential intelligence errors. 

Two gunmen opened fire at a Hanukkah celebration on Sunday evening, killing 15 people and wounding dozens more. 

A 24-year-old suspect remains in hospital under police guard, while his 50-year-old father, the other alleged offender, was shot dead. 

The younger man, who's suspected of orchestrating the attack, had previously been investigated by the country's security agency and hadn't been considered a threat. 

But Massey University Defence Studies Professor John Battersby says we shouldn't jump to conclusions until more details emerge. 

He told Andrew Dickens intelligence capabilities are always limited by the resources put into them. 

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