Walmart Security video clearly shows the youth with a rifle in his hands just before he was shot by police.
How would one tell without close inspection what kind of gun it was?
www.wksu.org/news/story/40578

I may be in the minority, but it seems to me that the only option is to shoot if the weapon is not dropped immediately.
What other options are there when the public is under possible threat?

Canada prohibits the open display of air rifles, BB-guns; both dangerous to the public.

The incident in Walmart could not happen in a Walmart in Canada where the items must be behind the counter and superintended.