Simon Bridges says it might be time to revisit an internet surveillance programme canned by the previous National-led Government.
Project Speargun, publicly revealed by US National Security Agency whistleblower Edward Snowden in 2014, was cancelled in 2013 according to then-Prime Minister John Key for being too intrusive.
"It was set too broadly," he told NZME in 2017. "What we ultimately did, when it comes to Speargun, in my opinion, I said it's set too far. I don't even want to see the business case."
Snowden claimed Project Speargun would have allowed the Government to tap into New Zealanders' communications.
Bridges, current National Party leader, has called for a royal commission of inquiry into the security and intelligence failings that allowed a white supremacist to amass an arsenal and shoot 100 people in Christchurch earlier this month, killing 50 of them. The alleged gunman wasn't on any watchlists here or in his native Australia.
There has also been criticism intelligence agencies have been too focused on the potential threat from Islamist extremists, and blind to that posed by the far-right.
Bridges told The AM Show on Friday he's not sure if a mass surveillance programme like Speargun would have uncovered the killer's plans.
"But I think what we can say is what I think is that we were overly cautious, and I think we need to revisit that."
He said at present, our intelligence agencies - the domestic-focused SIS and foreign spying GCSB - are "doing their work with both hands tied behind their back".
"Speargun was really about going on the highways and getting the traffic. What we've done is just gone down a few driveways... I can't say hand on heart it would have changed this, of course I can't, but I can say it would have made New Zealanders safer that we should be thinking more about our cybersecurity settings. At the moment we went down a few driveways. I reckon we need to go wider than that."
Speargun's replacement, Cortex, has a much narrower focus - protecting key institutions from cyberattack.
"The risk profile of New Zealand has changed, right?" said Bridges. "We've gone from low terrorist risk to high... You've got ISIS out there threatening, you've got a Turkish President showing this and inflaming crowds, you've got the risk of copy-catting. So we do need to look at these things. I'm not saying it's easy, but I think we need to think about change."