The Police should be able to sense if the merchandise person is credible and/or suspect.
If he is, then a photo lineup with the "POI" included and a positive ID by the merchandise person would give more than enough reason to re interview him. If they haven't done any of this than they are not following the obvious investigative process. I will give them the benefit of a doubt that they are capable of this, although I have some doubts which I will mention below. If the Police have already gone through these steps and the merchandiser could not ID the person I believe most of us are referring to, then they must either exclude him or find other connections, whatever they feel they are willing and able to do based on their belief of his involvement and importance to the case,i.e. polygraph etc..
As far as the sketch goes, there seems to be enough recognizable features (hair style,type of glasses) to make it more than just generic, I believe.
Also, after hearing the Sheriff's claim that most people at the party were drunk or high (paraphrase) it immediately caused me to question his judgement.
I admittedly have been drunk at crowded events and saw violent things happen, many years ago, but I would have had no difficulty describing people and actions at that time, well enough to be able to offer Police important enough information to lead them in the right direction. I doubt everyone there, even if all were drunk or high, which they wouldn't have ALL been, were all at the same level of intoxication, (even if so, individual perception and retention, is never equal) such that they weren't able to be reliable to any value.For the Sheriff to disregard witnesses (possibly numerous) who had been drinking or even smoking weed with such a blanket statement seems somewhat foolish and simplistic to me.