While the overall concept - cause a significant stock price drop, buy low, wait, and sell high - is at least somewhat sound, the implementation was way off.
First, he involved someone else who, obviously, had less to lose than he did.
Second, you probably want to target the supply chain rather than the retail stores for the best efficiency.
Finally, you want it to look like something that is Target's fault as opposed to some random act by a local nut-job.
If I were going to do something like this - which I wouldn't - the first thing I'd do is grow a nice, large batch of E.coli or some other similar, nasty but rarely fatal bug. Next, I'd get a good fake ID. Then, I'd get a part time job using that fake ID as a graveyard shift gopher - the kind of job that's easy to get because it doesn't pay much, there's high turnover, and they'll hire just about anyone without digging too deeply into their employment history - at one of their regional distribution centers. Finally - after figuring out when, where, and how to best deploy the bug out of sight from prying eyes and security cameras - I'd inject small amounts of the bug into various batches of produce, refrigerated, and frozen goods.
It would probably take longer to have a significant effect on stock prices but it would have the added benefit of scaring away customers nationwide instead of just one area.
