The government questioner was low key; the witness who took the stand yesterday was also matter of fact. But the testimony of Garry Norris from IBM Corp. — and the documents he brought to court with him — told the most explosive and comprehensive story to date of how Microsoft bullies competitors on price and other conditions of its Windows operating systems license.

Under questioning from Justice Department attorney Phillip R. Malone, Mr. Norris, an IBM manager, testified that IBM’s relationship with Microsoft was already “poor” and “somewhat contentious” when he moved into the job. Mr. Norris was the primary negotiator of IBM’s Windows license agreements with Microsoft from March 1995 to March 1997.