Key testimony was delivered Monday in the trial of the man accused of driving drunk and causing the death of a Nassau police officer.

James Ryan was allegedly intoxicated when police say he caused two accidents on the LIE back in October of 2012. Officer Joseph Olivieri was responding to those accidents when he was fatally struck by another driver, Francis Belizaire.

Ryan was charged with manslaughter, drunken driving and other charges. 

Belizaire took the stand Monday and testified that he swerved to avoid Ryan's car and struck Olivieri in the process.

"I was in shock, I didn't move," he recalled.

Ryan's defense attorney, Marc Gann, says Belizaire shouldn't have been driving at all because his license was revoked back in 1988.

On Tuesday, the defense will continue to cross-examine Belizaire. If convicted, Ryan faces eight to 25 years behind bars.