The arguments came midway through an eight-week trial in federal court in Salt Lake City and will continue late Monday.
Novell faced tough questioning from U.S. District Judge J. Frederick Motz, who said he did not believe the network software maker had shown enough evidence for a jury to decide the case. Motz said he was reserving a decision.
Novell argues that Microsoft co-founder Bill Gates ordered company engineers to reject WordPerfect as a Windows 95 application because he feared it was too good. WordPerfect's share plummeted from nearly 50 percent to less than 10 percent of the market as Microsoft's own office programs took hold.
Novell said it was forced to sell WordPerfect for a $1.2 billion loss two years later.
Microsoft lawyer David Tulchin said Gates decided against installing a WordPerfect program because it threatened to crash Windows and couldn't be fixed in time for the Windows 95 rollout. He argued that Novell's missed opportunity was its own fault, and that Microsoft had no obligation to give a competitor a leg up.
"Novell never complained to Microsoft," Tulchin said. "There's nothing in the evidence, no documents."
Novell attorney Jeff Johnson conceded that Microsoft was under no legal obligation to provide the keys to the Windows 95 operating system so Novell could prepare a compatible WordPerfect version. Microsoft, however, enticed Novell to work on a version, only to withdraw support months before Windows 95 hit the market, he said.
"We got stabbed in the back," Johnson said Friday.
Yet Motz challenged Novell to show evidence of the alleged subterfuge. He said he had nothing to go on but the assertion by a former Novell CEO who testified he took his complaints personally to Gates.
"Where are the letters, emails - anything?" Motz said.
If the trial proceeds, Gates is scheduled to testify in his company's defense.