Clearly, from just the standpoint of informing her viewers, the perpetrators are a large part of the Columbine story. This dilemma of Oprah's brings up an interesting dichotomy that I think much of the media faces whenever there is a tragedy of this sort.
To some extent, you have to investigate the killers or criminals and give them press or attention in order to get answers to "What were they thinking?" and "Why did they do it?" And isn't everyone wondering that when something like Columbine happens?
But then there is this guilt that comes along with the fascination. A self-imposed punishment for giving attention to the people who did wrong. And on top of that, I think, an even greater sense that it's wrong to give them any compassion.
I think these sensations appeal to the smaller part of our nature. What happened was wrong, without a doubt. The killers were responsible, without a doubt. But being curious about them is nothing to be guilty about. And extending compassion their way does not lessen the amount of compassion we have left over for the people they killed.
Compassion and attempts to understand do not mean we condone.