Wellll, that was a very different situation. Ted Kaczynski was not a leaker. They published it in the hope that someone would recognize it and identify him -- which is exactly what happened.
Of course I don't know what was in their hearts when they made the decision, but their public statement was to the contrary:
Donald E. Graham, The Post's publisher, and Arthur O. Sulzberger Jr., publisher of the New York Times, said they jointly decided to publish the document "for public safety reasons" after meeting last Wednesday with Attorney General Janet Reno and FBI Director Louis J. Freeh. [...]
"From the beginning, the two newspapers have consulted closely on the issue of whether to publish under the threat of violence. We have also consulted law enforcement officials," Graham and Sulzberger said in a joint statement. "Both the attorney general and the director of the Federal Bureau of Investigation have now recommended that we print this document for public safety reasons, and we have agreed to do so." [...]
"Neither paper would have printed this document for journalistic reasons," Graham said in an interview. "We thought there was an obvious public safety issue involved and therefore sought the advice of responsible federal officials. We are printing it for public safety reasons, not journalistic reasons." [0]
Okay, this doesn't explicitly support my impression that the possibility of getting a lead in the case was specifically suggested in prospect as a reason to publish, though some Wikipedia editor thinks that was the case ("[Freeh and Reno] recommended publication out of concern for public safety and in hopes that a reader could identify the author" [1]; it's not clear what citation this is based on). But it does seem to indicate that if their motives were as you suggest, they managed to keep that fact to themselves.
