At one point they were saying there might be two shooters, too. This seems to happen a lot in these cases, and it turns out that there was only one.
Whenever you have breaking news on a quickly developing story ... the reporters will receive a lot of misinformation from different sources that they have. This misinformation is typical because the story is developing and not everyone actually knows what the situation is, and even the sources have been told wrong information, because other people “just don’t know for sure” yet.
Actually, I’ve seen that it takes about one or two days for reporters to gather the actual facts of the matter. That’s just the way it goes.