To answer to the previous comment: finding a person knowing where he lives is quiet easy. A name on the mail box, any letter or paper in his home will give his identity. Belmondo is in the villain's house alone. OK, they could show us, but we can imagine.
What I think is worse in the story is that the "Epervier" would NEVER have let live the young man who helps him in the jewelry robbery. He kills everyone, except this young man, leaving him only injured. It's nonsense, this particular villain could not do that. He was not in such a hurry, he takes time to kill the two cops and doesn't take the time to shoot the kid! And also it's using a very bad facility in the scenario than to just make this young man, the only one the "Epervier" let live knew exactly who he was and where he lived...
I think the scenario would have been better if either the story was only between the Alpagueur and the Epervier OR between the Alpagueur and the Prison story. Two stories in the same movie makes one of them writtent quickly. I would have loved to see the Epervier character a little more explained, this was an interesting character that was underused in the movie and lost for another scenario.