Why is the colonel blanking the questions with sketches?

I think that he's removing unrelated information.

I'm completely unfamiliar with the book and film, but after searching the Google Book I found following passage that seems to match the image/description above:

The top copy of Kowalski's confession came with the coffe. The first time he read the twenty-six pages of the dossier quickly, trying to grasp the gist of what the demented legionnaire had been saying. Something in the middle caught his eye, causing him to frown, but he read on the end without a pause.

His second reading was slower, more cautious, giving greater concentration to each paragraph. The third time he took a a black felt-nib pen from the tray int he front of the blotter and read even more slowly, drawing the thick black line of the ink through the words and passages relating to Sylvie, Luke something, Indo-China, Algeria, JoJo, Kovacs, Corsican bastards, the Legion. All these he understood, and they did not interest him.