"And how can you do that?"
"It is a matter of means, opportunity, and motive. You had the means of killing Jander - the theoretical ability to so, manipulate him that he would end in a mental freeze-out. But did you have the opportunity? He was your robot, in that you designed his brain paths and supervised his construction, but was he in your actual possession at the time of the mental freeze-out?"
"No, as a matter of fact. He was in the possession of another."
"For how long?"
"About eight months - or a little over half of one of your years."
"Ah. It's an interesting point. Were you with him - or near him - at the time of his destruction? Could you have reached him? In short, can we demonstrate the fact that you were so far from him - or so out of touch with, him - that it is not reasonable to suppose that you could have done the deed at the time it is supposed to have been done?"
Fastolfe said, "That, I'm afraid, is impossible. There is a rather broad interval of time during which the deed might have been done. There are no robotic changes after destruction equivalent to rigor mortis or decay in a human being. We can only say that, at a certain time, Jander was known to be in operation and, at a certain other time, he was known not to be in operation. Between the two was a stretch of about eight hours. For that period, I have no alibi."
"None? - During that time, Dr. Fastolfe, what were you doing?"
"I was here, in my establishment."
"Your robots were surely aware, perhaps, that you were here and could bear witness."
"They were certainly aware, but they cannot bear witness in any legal sense and on that day Fanya was off on business of her own."
"Does Fanya share your knowledge of robotics, by the way?"
Fastolfe indulged in a wry smile. "She knows less than you do. - Besides, none of this matters."
"Why not?"
Fastolfe's patience was clearly beginning to stretch to the cracking point. "My dear Mr. Baley, this was not a matter of close-range physical assault, such as my recent pretended attack on you. What happened to Jander did not require my physical presence. As it happens, although not actually in my establishment, Jander was not far away geographically, but it wouldn't have mattered if he were on the other side of Aurora. I could always reach him electronically and could, by the orders I gave him and the responses I could educe, send him into mental freeze-out. The crucial step would not even necessarily require much in the way of time -
Baley said at once, "It's a short process, then, one that someone else might move through by chance, while intending something perfectly routine?"
"No!" said Fastolfe. "For Aurora's sake, Earthman, let me talk. I've already told you that's not the case. Inducing mental freeze-out in Jander would be a long and complicated and tortuous process, requiring the greatest understanding and wit, and could be done by no one accidentally, without incredible and long-continued coincidence. There would be far less chance, of accidental progress over that enormously complex route than of spontaneous mental freeze-out, if my mathematical reasoning were only accepted.
"However, if I wished to induce mental freeze-out, I could carefully produce changes and reactions, little by little, over a period of weeks, months, even years, until I had brought Jander to the very point of destruction. And at no time in that process would he show any signs of being at the edge of catastrophe, just as you could approach closer and closer to a precipice in the dark and yet feel no loss in firmness of footing whatever, even at the very edge. Once I had brought him to the very brink, however - the lip of the precipice - a single remark from me would send him over. It is that final step that would take but a moment of time. You see?"
Baley tightened his lips. There was no use trying to mask his disappointment. "In short, then, you had the opportunity."
"Anyone would have had the opportunity. Anyone on Aurora, provided he or she had the necessary ability."
"And only you have the necessary ability."
"I'm afraid so."
"Which brings us to motive, Dr. Fastolfe."
"And it's there that we might be able to make a good case. These humaniform robots are yours. They are based on your theory and you were involved in their construction at every step of the way, even if Dr. Sarton supervised that construction. They exist because of you and only because of you. You have spoken of Daneel as your 'first-born.' They are your creations, your children, your gift to humanity, your hold on immortality." (Baley felt himself growing eloquent and, for a moment, imagined himself to be addressing a Board of Inquiry.) "Why on Earth - or Aurora, rather - why on Aurora should you undo this work? Why should you destroy a life you have produced by a miracle of mental labor?"
Fastolfe looked wanly amused. "Why, Mr. Baley, you know nothing about it. How can you possibly know that my theory was the result of a miracle of mental labor? It might have been the very dull extension of an equation that anyone might have accomplished but which none had bothered to do before me."
"I think not," said Baley, endeavoring to cool down. "If no one but you can understand the humaniform brain well enough to destroy it, then I think it likely that no one but you can understand it well enough to create it. Can you deny that?"
Fastolfe shook his head. "No, I won't deny that. And yet, Mr. Baley - his face grew grimmer than it had - been since they had met - your careful analysis is succeeding only in making matters far worse for us. We have already decided that I am the only one with the means and the opportunity. As it happens, I also have a motive - the best motive in the world and my enemies know it. How on Earth, then, to quote you, or on Aurora, or on anywhere - are we going to prove I didn't do it?"