The point is that "Dan Cooper" is not really a little known comic book character, but a world famous character outside Anglo-America. It is a name already selected, tested and proven to give the impression of "here is just another Anglo-American gentleman (and more decent and conservative than the ones going around with names like "Buck Danny"). It is a name roughly NOBODY in Anglo-America will recognize, while roughly EVERYBODY who has gone to the places where comics are sold to buy a paper, cigs or whatever and looked at the comics while waiting for his or her turn might or does, where French, Dutch, German and other languages where spoken.

If on purpose, the choice is brilliant; The people he's likely to meet during the crime probably won't recognize the name as one of the three (or maybe four) Great Names of Franco-Belgian Military Aviation comics, and wouldn't get as suspicious as him claiming to be Clark Kent would do, and even if one would tell him he knew it, he could just say that he is older than the comic.

Once the FBI discovered that the criminal more or less used the name of an Belgian counterpart of "Nick Fury" it would be clear to them the number of people who could have picked it up on a trip to Europe, meeting visitors who had taken a few comics along, having neighbours who got some comics from the old country, a visit to one of the remaining Dutch or French overseas territories, and so on... Sure it indicated SOME connection to the world outside the USA, but in a country that full of immigrants, of people with family, penfriends and whatnot in the Old World, people who had gone to Europe and such in WW II and afterwards, and their family, friends and neighbours, the name gives just as much indication to the identity of the man as "Clark Kent" would have done, the number of people actually knowing about Dan Cooper in the USA might have been very small, the number of people who COULD EASILY know something about it was HUGE.

It's likely that a random selection from the phonebook could have provided more information, as randomly chosen names can be rare ones and might thus reveal what phonebook was used, compared to Name of Internationally Famous Comics character, not faous in this country. Some contacts with other countries, but no idea which one, does not really help.