I won't buy any rumors until about 2 or 3 hours by now; sure, ISIS can claim this. What else would they do with an incident like this.
Then, some will say, don't trust CNN, ABC, etc.; maybe but I don't think the whole media can be bamboozled.
This tragedy only happened a few hours ago. Police, FBI and who knows how many other agencies have only begun their investigations. They are searching the perp's home and will be picking his whole life apart for some time. Heck, even the number of dead and injured can't even be agreed upon yet.
So really, it's not wise to believe every story you hear. I heard that at the time of the incident, rumors were spreading of more than one shooter, more than one shooting location, and that there were several bombs set to go off around the city.
All these stories are designed to create more fear and panic. Some very sick people get their jollies from stirring up sh!t. So let's just wait till there are more confirmed details.