Omaha shooter used an SKS not an AK47 of any variety.
The media and the police chief got things mixed up as usual.
It appears that he used a semi auto version of the AK family known as the MAK-90. I have not seen definitive documents, but a freeper spoke definitively of it.
Have an "official" source for that? The pictures I saw sure looked more like an AK profile to me. Not that it matters much.