The Case Behind the Case
But why did this case end up in a patent court instead of a copyright court? The reason is that, in a strictly legal sense, a charge of patent infringement was the trigger for the legal actions that led to this case being heard. And curiously, it was Jacobsen who was accused of violating Katzer's patent, although it was Jacobsen who filed the suit against Katzer. The law is indeed a curious thing.
In a sense, nobody really knows what the law is until a case is brought and a judge gets to rule on specific facts. And a case gets brought when some individual chooses to do so, meaning that the detailed facts in a particular case have a lot to do with what elements of the law come to the judge's attention and therefore how the nuances of interpretation play out. But free and open-source software was waiting for its day in court, and this particular case got it there.
Jacobsen works at Lawrence Livermore National Laboratory and is a model train enthusiast. He is the principle developer of the JMRI Project (jmri.sourceforge.net), an open-source project devoted to his Java Model Railroad Interface software. Jacobsen knew he had a problem when he started getting letters from Katzer alleging violation of Katzer's patent, culminating in a request for something over $200,000.
Jacobsen looked at Katzer's software and decided he'd better strike first. He file a preemptive suit against Katzer, claiming that Katzer's patent was fraudulently obtained, invalid, and unenforceable; and that in fact Katzer had improperly incorporated part of Jacobsen's JMRI software in the code for which he claimed a patent. He also charged Katzer with cybersquatting and a few other offenses. And he made an online plea to other developers to help him nail down the prior art to debunk Katzer's patent. Open-source lawyers and developers jumped on board, helping him make his case.
And Jacobsen v Katzer became the test case for the enforceability of copyleft licenses.