The transplant
If all Frankenstein had to do to fix the brain of his colleague was to drill a hole and release the pressure, why was it necessary to also put the brain in another body?
shareI'm pretty sure it was mentioned Brandt suffered a severe heart attack when they tried to get him out of the asylum. Frankenstein didn't think much of his chances of survival (especially after brain surgery), so he thought the transplant was his best chance of getting Brandt to give him the information he wanted.
shareCorrect. I just finished watching it, that's exactly what happened. Karl diagnoses a severe heart attack. The baron surmises that he will only be able to keep Brandt alive for '2 or 3 days' and that the brain surgery he planned would now be impossible. So he improvises and decides to perform the brain transplant surgery first, putting Brandt's brain into a host body that won't die so quickly.
With all of this going on, I had forgotten what Brandt's secret was that the baron wanted so badly. I rewound the DVR and found that the baron told Karl the breakthrough that Brandt had found, that he (the baron) had not, was the ability to put a brain on ice, or in effect, freeze it for the future. If the baron knew how to do this, then he would not have needed another body for Brandt's brain (at least, not immediately). But he did not yet know; he only knew how to perform 'live' brain transplants, but did not yet know how to preserve a brain for a future operation. Thus the need for a fresh body to keep Brandt's brain alive, until he can learn the secret. What exactly the baron planned to do with Brandt/Richter after he learned the secret, he never said, but it's safe to say he probably would have disposed of him in a discreet manner.