Giuliani at the convention. (YouTube/ABC-15)

One of the terrorists who killed an elderly priest in France this week had been placed under house arrest after trying to travel to Syria last year. An electronic monitor that tracked his movement was temporarily turned off, according to Sky News, during which time he helped kill Father Jacques Hamel.

Rudy Giuliani, the former mayor of New York and an advisor to the campaign of Donald Trump, appeared at a Republican National Committee event on Wednesday, after which he was asked about the prospect of introducing a similar monitoring system for those on the terror watch list.

"I would think that's an excellent idea," Giuliani told NJ.com's Claude Brodesser-Akner. "If you're on the terror watch list, I should know you're on the terror watch list. You're on there for a reason."

Giuliani's built his post-mayoral career on issues of security, appearing in ads for LifeLock and consulting on the subject on the basis of the drop in New York's crime rate under his tenure. (That drop began prior to his taking office.) Last week, Giuliani talked about security at the Republican convention.

"Donald Trump has said the first step in defeating our enemies is to identify them properly and see the connections between them, so we can find them and catch them," Giuliani said. While he was mayor, he introduced a system to track and monitor Muslims in New York that was critiqued as both ineffective and a violation of people's civil rights. The program has been shut down.

It's clear that a proposal to mandate some sort of ankle-bracelet-style program for people on the terror watch list would be a much more expansive violation of civil liberties. When a proposal to ban guns to people on the watch list was proposed last year, we spoke with a former attorney with the American Civil Liberties Union who pointed out that the list was both overly broad and full of holes. There are various levels at which the government keeps tabs on suspects, including the no-fly list. But it includes thousands of people who, without having been subject to any due process, would suddenly be tracked by the government.

FBI Director James Comey opposed the no-fly list gun ban specifically because he didn't want people to know who was on the terror watchlist.

"It's a little bit challenging for us because 'known or suspected' means it hasn't been adjudicated in every case that somebody is a terrorist," Comey said during a Senate subcommittee meeting last year. "It's somebody we're investigating, so we don't want to, obviously, blow our investigation."

Putting an ankle bracelet or other electronic system on someone without tipping them off would be a logistical challenge even if a court signed off on it -- which seems unlikely.

We'll note that this was one question asked after a campaign event, and we shouldn't assume that Giuliani has given it a whole lot of thought -- or that this has anything to do with the policy proposals of the Trump campaign.

It's worth noting one other easy rebuttal, though: In France, it didn't work.