Officials had considered removing the cap because pressure readings had indicated a leak elsewhere.
That cap ended up stopping the oil flow.
Scientist Paul Hsieh created a model to explain what was happening under the cap and how - despite low pressure readings - there was no leak. He was convinced the containment cap wouldn't blow.
More than 170 million gallons of oil gushed into the Gulf from April 20 to July 15.
The Associated Press Contributed to this report.