In this portion of his speech, Fetyukovich sets out to establish a plausible explanation for Smerdyakov as Fyodor's murderer.
After dismissing Grigory's testimony (a little too much vodka), Fetyukovich proceeds to tell the court about his own impressions on meeting Smerdyakov. In contrast to the prosecutor's description of Smerdyakov as a weak, bullied man, Fetyukovich paints a picture of him as a wily, spiteful man who knew exactly what he was doing when he set up Dmitri.
Fetyukovich then points out that Smerdyakov had plenty of time to commit Fyodor's murder between the time Dmitri attacked Grigory and the time Grigory fully recovered consciousness.
At this point Fetyukovich takes on a "heartfelt" voice, in contrast to the calm, sensible way he had proceeded thus far.