Having dealt with a few hundred unfair dismissals I can promise you all that there is going to be much more to this than meets the eye.
It could be that there has been a history of items going "missing" and security was asked to do an "impromptu" bag check to see if they could find anything.
On another note I don't think anyone has assumed this person is guilty. I think the vast majority of opinion is that
IF he/she is guilty then there is no sympathy.
As I stated earlier, if the items in question are only the two biscuits then he/she will more than likely win the unfair dismissal claim and get their job back.
BUT I think the two oreo story is just the tip of the iceberg.