How do people figure out John and Holly McClane's identities in the first Die Hard?

Question

Originally, the protagonist in Die Hard says his name is "Roy" in an effort to conceal his identity.

Somewhere down the line, his ally Al Powell and everyone else outside know he is John McClane. How?

And later on the boss even figures out that John's wife is among the hostages, while not noticing it previously. How does he suddenly know that?

Based on comment and based on my first view of the movie, it has something to do with Ellis talking to the bad guy about John. It wasn't very clear though.

Also if Ellis talks to the boss, then how come the cops know it too? So a related question will be, how are John, the terrorists, and the cops in the same frequency?

Basically, how do Hans, and Powell, start realizing that Roy is John McLane?

Answer 1

Ellis, who believes he's smarter than everyone else, asks to speak to Hans. When brought to the office, he tells Hans, "Is the big guy upstairs ruining everything? I can give him to you."

It's presumed that between that scene and when Hans calls John by name that Ellis has told them McClane's identity, but left out his relationship to Holly. Instead, he said something to the effect that they are friends from school, and McClane was his guest. This was all stated by Ellis while McClane was telling him he'd made a big mistake and to tell them he didn't know John.

As for the police hearing this, that's a little bit harder to give a rational explanation for. They may have switched to a police channel given that McClane had obviously been in contact with them and figured he'd be on that channel. But remember; Hans' plan was to involve the police and the FBI from the start. It was the only way to get the electricity cut to the building, which is what was keeping the 7th wall of security to the vault active.

Al did not know John McClane's name until that radio conversation between John and Hans. However, he did suspect he was a cop. Nothing beyond that was known by Al and company until that conversation.

Answer 2

There are nine key players in this drama. They each find out John McClane's true identity in different ways and at different times.

• Holly (John's Wife)
  Knows John from before the film starts

HOLLY: Didn't we have this same conversation in July? Damn it, John, there was an opportunity out here -- I had to take it --

• Argyle (a Chauffeur)
  John introduces himself in scene 7

As he waits he beats out a rhythmn on a "Nakatomi Corporation" card with J. McCLANE written on it in magic marker. McClane pauses in front of him, unsure.

MCCLANE: I'm John McClane.

• Takagi (Holly's Boss)
  Recognises John as he arrives at the party

TAKAGI: I've spent half my life on airplanes, I can recognize someone who just got off one. (shaking hands) I'm Joe Takagi, Mr. McClane. I have...something to do with this company.

• Ellis (Holly's Co-worker)
  Takagi introduces John in scene 16

TAKAGI: (as Ellis rises) Ellis, this is John McClane...(with meaning) Holly's policeman?

• Hans Gruber (a Thief)
  Told John's identity by Ellis (off-camera) between scene 230 and scene 232

HANS: (dryly): I must have missed 60 Minutes. What are you saying?

ELLIS: The guy upstairs who's fucking things up? I can give him to you.

• Dick Thornburg (a Reporter)
  Hears Gruber using John's name on the CB radio in scene 233.

HANS' VOICE (o.s., on CB) Touching, cowboy, touching. (pause) Or should I call you Mister McClane? Mister officer John McClane of the NYPD?

McClane FREEZES. How much do they know?

THORNBURG - IN TRAILER

Reacts, gleeful, writes down the name.

• Powell (a Policeman), Johnson (an FBI Agent) and Johnson (an FBI Agent, no relation)
  Overheard the conversation between Gruber and McClane in scene 233. Note that at this point in the script everyone knows McClane's identity.

EXT. BUILDING

Powell fends off Robinson, who wants the CB.

ROBINSON: Goddamn, didn't you hear him! He practically pulled the goddamned trigger himself -- he gave that man to them --

---

As to Holly's identity as John's wife, Gruber already has his suspicions that John isn't there as Ellis' guest in scene 239.

HANS: Hear that? Talk to me, where are my detonators. Where are they or shall I shoot another one? Sooner or later...
(taking a shot)
...I might get to someone you do care about.

He finally works it out in Scene 324 when he see Thornburg on TV talking to her children and her policeman husband. He recognises Lucy McClane from her photos in Holly's office.

THORNBURG: (to the children) ...because he's a very brave policeman. And your mom has shown just as much courage. But is there something you would like to say to them if they're watching?

John Jr. says nothing, but Lucy looks at the camera.

LUCY: Come home.

Holly struggles to stay composed...can't. She slowly turns her head, looks at Hans.

HER P.O.V. - HANS

He's looking away from us, at the picture of the children on her desk. He turns back and looks at her. He smiles.

HANS: Mrs. McClane. How nice to make your acquaintance.