How did Alexander Pierce know that Sitwell blabbed about Zola's algorithm? I mean Sitwell told everything about Zola on the rooftop and there's no way that any HYDRA members would have found out.
Considering the company Sitwell was with I think Pierce just assumed that they got Sitwell to talk, whether it was about Zola‘s algorithm or hydra didn’t matter, Sitwell talked and like he said “Hydra doesn’t like leaks”