This blog post in National Review points out that the Oregon mass murderer obtained all of his guns legally, then snarkily concludes:
Presumably this will stop precisely nobody linking the incident to their preferred firearms-purchasing reforms.Of course, if he had obtained the guns illegally, National Review and other conservatives would be saying that shows the gun laws were ineffective at stopping murder, because murderers brazenly violate the law.
That the current laws allowed him to obtain the guns is consistent with those who say the laws should make it harder to obtain guns.
Now, I don't know whether there's any good reform that would have stopped him from obtaining his guns, since this isn't a big issue of mine and I'm just not very well-informed about it. But I can state the obvious: pointing out that the law allowed a mass murderer to possess the gun he used to kill people does not make the case against cracking down on gun possession!