SAN FRANCISCO — Prosecutors and defense lawyers tussled for roughly three hours on Friday over evidence in the trial of David Nosal, a former Korn/Ferry International executive charged with breaking into the computer system of his onetime employer and stealing trade secrets.

In their closing arguments to the jury, the two sides quarreled over which witnesses jurors should believe, gave contrasting views of the documents in evidence, and put their spin on the key legal concepts, such as what constitutes a trade secret and the standard for "unauthorized access" to a computer.