In order for science to establish that God does not exist, it would be necessary to determine which observations we would make if there were a God, and which observations we would make if there were not a God. However, these claims about what we would observe if God does or does not exist, are philosophical claims, not scientific claims. Therefore science alone could not disprove the existence of God.
van Inwagen, Peter
"Can Science Disprove the Existence of God?,"
Philosophic Exchange: Vol. 34
, Article 3.
Available at: http://digitalcommons.brockport.edu/phil_ex/vol34/iss1/3