This is a rush transcript from "On the Record," December 15, 2015. This copy may not be in its final form and may be updated.
GRETA VAN SUSTEREN, FOX NEWS HOST: Today's terror attacks point out very differently on the east coast. In New York City, officials say they received the same exact threat as the L.A. schools but quickly deemed it not credible.
(BEGIN VIDEO CLIP)
BILL BRATTON, NEW YORK CITY POLICE COMMISSIONER: We affirm that we do have an investigation underway, but it's an investigation into a hoax, which we strongly believe that the email that was received in New York City, which is similar and almost exactly the same as received in other locals, specifically Los Angeles that we do not see that as a credible terrorist threat and we are investigating it as a hoax.
We believe that the email originated overseas. The language in the email would lead us to believe that this is not a Jihadiist initiative. For example, that Allah was not spelled with a capital "A." That would be incredible to think that any Jihadist would not spell Allah with a capital "A."
(END VIDEO CLIP)
VAN SUSTEREN: So how do you know if a threat is real or fake? Whether to act or not.
Former New York City Mayor Rudy Giuliani goes ON THE RECORD.
Good evening, sir.
RUDY GIULIANI, FORMER NEW YORK CITY MAYOR: Good evening, Greta.
VAN SUSTEREN: Mayor, how do you know when to act, whether something is real, not real, credible, incredible?
GIULIANI: It comes from a great deal of experience. It comes from a tremendous amount of knowledge and Bill Bratton has it. But it's always a gamble, right? I mean, Bill could have been wrong. He was right. So whenever I got these threats and after September 11th, I would get about 150 a day for about six weeks. I would turn it over to my police department and they would analyze it in great detail. And they would give me a recommendation, we should protect this building, we should evacuate this building or we shouldn't.
And the fact is I hate to sound terribly parochial, but the New York City Police Department is just ahead of everybody else in being able to figure this out. And I'm really not at liberty to tell you all the things they look to figure it out because we have been under threat for so long going back to my administration, Bloomberg's and now De Blasio's with Bratton there, there is just a little more expertise in the N.Y.P.D. than there is any place else just because we have been targeted more often.
VAN SUSTEREN: I guess that they -- I know there is somewhat an attention on the fact that "A" wasn't capitalize in Allah. And I think to myself, a lot of illiterate Jihadist out there and they might not know the -- that's not --
GIULIANI: I can tell you, Greta, there was more to it than that.
VAN SUSTEREN: OK. All right. The only one asking -- now, New York decided that it was a hoax early on or concluded. L.A. didn't. If L.A. hadn't acted and shut down the schools, is it likely that we would have heard about the credible -- would have heard about the threat in New York? Or would that have been kept quiet because it was deemed not credible?
GIULIANI: No. I think we would have probably heard about it and I think L.A. -- you know, given what happened in San Bernardino, and given the trauma they are going through right now, I have no objection to what they did.
What you said before is absolutely correct. Err on the side of safety. When you gain more expertise with this, you can make more sort of informed choices, but God Almighty, I made a couple of times. I made choices not to protect things and I just prayed that I was right that I was getting the right information from the police department. Because God forbid you say no and a child gets killed, that's going to live with you for the rest of your life. So I have no problem with what L.A. did today.
VAN SUSTEREN: And it sure is a lot easier with 20/20 hindsight what's this issue could have made. You know, that's the problem with this business.
GIULIANI: The people here are the bad people -- are not the people in L.A., are not the people in New York and not the FBI and not the school's people. It's these monsters who are doing this. And I kind of come out where Catherine Herridge did.
VAN SUSTEREN: Which is?
GIULIANI: I have a suspicion this was a probe. I don't think this is a total hoax. I think this was a kind of a probe to figure out how we're going to react. Not an absolute hoax. They weren't going to carry out this attack today, but I think they were testing us.
VAN SUSTEREN: Well, I hope then as your old business and my old business about.
GIULIANI: That's my gut.
VAN SUSTEREN: .In criminal court, I hope that there is a quick arrest and we show them what justice is. We'll don't get copy cats and we stop this probe.
GIULIANI: I hope sO. I hope so, too. But I think, I think we should take this seriously. We should not just write it off. I think they are testing us.
VAN SUSTEREN: Mayor, always nice to see you. Thank you for joining us, sir.
GIULIANI: Thank you.