There are few, rare stories in the newspaper that could make a man shake violently, and then look so sick and panic stricken. As you're imagining what crimes Garfield must have committed, remember Jon is already aware of his friend's history of destruction of property, assault, theft, and animal-murder. So this must be something worse. Consider, given the state of our world, war-torn and blood-soaked, how serious the antics of a single cat would have to be to make even Page Eight of the paper. Whatever the offense, Garfield is not only remorseless but proud. Combined with his sarcastic wit, and obesity, Garfield may be the late 20th century's Oscar Wilde.
To be less ominous - or more?- Jon's response is partially because the story must include an eye-witness identification of Garfield.
The photo revealed when Jon lowers the paper is what draws the attention of any Garfield obsessive: is it a blurry silhouette of Garfield captured on film by a witness? The twin lumps depicted could be Garfield's rounded ears... or could be the same kind of non-specific-indicator-of-a-photograph that is the Three Lump front-page news.
While Garfield frequently mentally chastises Jon for being boring, at the opening of today's strip the cat is sitting at the table staring off into space, doing absolutely nothing. It's important that the story is about Garfield doing something unspeakably exciting and scandalous, but all that occurs within the narrative space of the strip is Garfield staring off blankly while Jon reads. That's the Garfield way: it may be a universe of horrors and those long, long stretches of nothing, those are the worst of all.