Why is Paulie so easily suspected?

Question

Every time I watch The Godfather I feel a little bad for Paulie.

He is quickly suspected of treachery, just for being sick the day of Vito Corleone's failed attempted murder. The result of not being able to work was his replacement by incompetent Fredo.

I know it's a common trope in these movies that they don't believe in coincidences... but what if?

Is there some elements that prove that Paulie really sold the Don? Isn't the job of Corleone Family's HR to replace a sick driver by another competent man?

Answer 1

No...they don't believe in co-incidences but they're not conclusive.

Paulie Gatto had been sick before but still...

So, they checked...the novel makes this clear.

Sonny said, “We have people in the telephone company and they tracked down all of Paulie’s phone calls in and out. Clemenza’s too. On the three days Paulie was sick this month he got a call from a street booth across from the old man’s building. Today too. They were checking to see if Paulie was coming down or somebody was being sent down to take his place. Or for some other reason. It doesn’t matter.” Sonny shrugged. “Thank God it was Paulie. We’ll need Clemenza bad.”

^{The Godfather - Mario Puzo}