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[Big Hero 6] Question about Dr. Callaghan (full spoilers)

I'm utterly confused about Dr. Callaghan's plan and his approach towards executing it. When he was walking around the science expo, was he prepared to steal a piece of tech that could successfully destroy Krei, and was he fully committed to fake his own death at a moment's notice? He didn't know Hiro was going to bring tech that could be a powerful weapon. When he got dressed for that evening event, what was going through his mind? Did he have the building rigged to explode, or did he have some convenient device that could quickly start an inferno so intense that he would stand no chance of being rescued? Did firefighters not find it odd that they couldn't find his body afterwards?

Even more confusing, if Callaghan was so absolutely consumed by his hatred for Krei, why didn't he just wait for him to arrive that night and stab him from behind? Or do the same thing months earlier? He obviously had the means to rig a building for either a fire or an explosion very quickly. Why didn't he just get a tour of Krei's new building and explode it?

You might say that Callaghan wanted to kill Krei in a method that would guarantee his anonymity, but one could easily argue that the plan he chose was far less anonymous than the stab-in-the-back technique. For one, tens of thousands of people in Sanfrantokyo would have recorded the masked Callaghan, and dozens of respectable, trustworthy students and professionals would later come forward and say that the only place they saw that tech before was at an expo in which only two people died: Tadashi Hamada and Robert Callaghan. Even if the police didn't make this connection, however, after Callaghan successfully executed his plan it's not like he could just stroll back onto campus.

He also had an insufficient number of microbots to execute his plan, and had to manufacture more. With this in mind, why didn't he just steal Hiro's idea at his leisure, and then produce the microbots in secret? He would then have an alibi and not have to incur the obvious risks of trusting a brand new technology to save his life in a broiling inferno. If this was a crime of passion, perhaps sparked by Callaghan unexpectedly running into Krei, all it would've taken for Callaghan to enact his plan is to steal the neurotransmitter and a handful of microbots, and he already had access to both of these. If killing Krei using the poetic justice of the Stargate was absolutely essential to his plan, it still doesn't explain why he didn't just ramp up manufacturing in his free time. Also, withdrawing money from your ATM and purchasing manufacturing equipment tends to raise eyebrows when you're supposed to be dead. (And stealing it is perhaps even riskier.)
gpt
Consider this theory:

**Callaghan's entire plan (burn down expo, steal microbots, manufacture microbots, bring down Krei) was all accidental and ad-hoc.**

Callaghan had (mostly) moved on with his life. He was a successful professor, running a very popular program at a prestigious school. This is not the life of a man bent on revenge. He sees Hiro, young, with lots of spirit and potential, and he has just invented a rather spectacular, world-changing, invention.

Then in walks Krei (obviously uninvited). Krei makes a bee-line for Hiro: he wants those microbots. While Callaghan calmly deflects Krei, the entire exchange had to make him wonder. He knows (or at least believes) Krei will do whatever is necessary to get those microbots. He also might be worried that Hiro will eventually cave to pressure. The microbots are a great invention but they can't fall into the hands of a man like Krei; more people will just die. He has to destroy them.

Be begins trying to destroy them when something goes wrong. A fire starts and he can't contain it. He manages to survive/escape but then realizes that Tadashi died trying to save him. He's distraught. But rather than accept blame for his reckless actions, he blames Krei. This is all Krei's fault. Once again Krei has robbed him of someone whom he cared for. Krei must be stopped. Not just stopped, but publicly exposed. Not just Krei, but his entire enterprise. But how?

As he stands among the rubble of the rubble of the expo he looks down into his clenched fist and opens it:

Inside is a microbot.