• With: Remi Spencer, KT McFarland

    This is a rush transcript from "Your World," October 7, 2014. This copy may not be in its final form and may be updated.

    (BEGIN VIDEO CLIP)

    QUESTION: Is there anything you want to say on your son's behalf?

    QUESTION: Would you like to say anything on your son's behalf in his defense?

    QUESTION: Is there anything you want to say, sir?

    (END VIDEO CLIP)

    NEIL CAVUTO, HOST: It's got to be tough for parents. Right? No comment. But did they know anything at all?

    The FBI says 19-year-old Mohammed Khan left a letter for his mom and dad telling them not to contact authorities about his plans to join ISIS. He even reportedly invited them to come.

    But even if they knew what their son was allegedly doing, attorney Remi Spencer says we really can't do anything legally about it. Fox national security analyst K.T. McFarland says, well, if that's the case, we should. Remi, to you first. You think that there's no legal grounds to pursue.

    REMI SPENCER, FORMER PROSECUTOR: You know, I think that we have a moral obligation to alert the authorities when we know or suspect something like this.

    CAVUTO: So, if you knew somebody in your family was up to something nefarious?

    SPENCER: Well, I would like to think no one in my family would do anything like this.

    CAVUTO: Well, I don't know.

    SPENCER: But, yes, I would report something.

    CAVUTO: Really?

    SPENCER: If I saw it, I would report it.

    Now, the law, as it's written right now, does not allow people to support a known terrorist organization. The laws were created to basically prevent financial crimes, so that people wouldn't be sending money to known terrorist organizations.

    CAVUTO: Right. Right.

    SPENCER: And it is sort of a stretch of that law that we are prosecuting people for joining known terrorist organizations.

    In this case of this gentleman from the Midwest, it's an attempt to support ISIS because he was on his way. He hadn't committed a crime, so his parents really couldn't be prosecuted under any kind of criminal...

    CAVUTO: Well, that assumes that they knew any of this.

    SPENCER: That's right.

    CAVUTO: But you say what, K.T., that extenuating circumstances, national security circumstances dictate what?

    K.T. MCFARLAND, FORMER DEPUTY ASSISTANT SECRETARY OF DEFENSE: Well, the problem is, there may not be a law now, but we better find one, because this is a trend. This will continue.

    The Holy Grail of terrorist recruiting is to get a young man who has a passport of a country that he can move around in, he can enter, he can leave. Here's what happens. I talked to a former Al Qaeda recruiter, a guy who has seen the light and now is a good guy.

    He said that here's how the recruiters do it. They have a charismatic young 20 -- late 20-year-old. He goes to the mosque. He goes to the youth group. He looks around. He finds the 12-, 13-year-old boy. He gets several of them today. They join the equivalent of the Boy Scouts. They go on camping trip together. They go to movies together. They get to be sort of a pack together.

    They study the Koran together, and then they look to see somebody who is vulnerable, who is taking the religion part of it to the next level, and then they isolate him out, they recruit him, they convince him that he has got a mission, and then they send him on a round-trip ticket to jihad.

    CAVUTO: So, let's say...

    MCFARLAND: So, the all-expenses-paid tour.

    CAVUTO: ... it's at that point the parents are aware you're associating with some weird dude, we don't who it is.

    MCFARLAND: Right.

    CAVUTO: But we don't like it.

    SPENCER: Well, the -- right now, the way the law is written, it's how far can the federal agents and our U.S. attorneys stretch it to say that the parents are an accomplice? Are they helping their son support or fight with a known...

    CAVUTO: But what if the parents are just suspicious of the characters with whom he is hanging out?

    SPENCER: No, there's no criminal law that requires you to come forward. You don't have...

    (CROSSTALK)

    CAVUTO: But if the dad or mom knows, all right, this guy, I'm seeing some of these exchanges with you, son, he is -- he is from ISIS?

    SPENCER: Well, think about it in more local terms. If you know that somebody is a gang member in your neighborhood, do you have a criminal, legal obligation to tell the police? No, you don't.

    CAVUTO: So, you would -- you would leave it at, tell your kid not to?