The point of the trial wasn't to deliver justice but to eliminate Beria. Khrushchev had to consolidate power first.
Apocryphal anecdote:
Following Stalin's death, Nikita Khrushchev gave a speech to the Politburo denouncing Stalin's policies. A few minutes into Khrushchev's diatribe, somebody shouted out, "Why didn't you challenge him then, the way you are now?"
The room fell silent, as Khrushchev angrily swept the audience with his glare. "Who said that?" he asked in a reasoned voice. Silence.
"Who said that?" Khrushchev demanded, leaning forward. Silence.
Pounding his fist on the podium to accent each word, he screamed, "Who - said - that?" Still no answer.
Finally, after a long and strained silence, the elected politicians in the room fearful to even cough, a corner of Khrushchev's mouth lifted into a smile.
"Now you know," he said with a chuckle, "why I did not speak up against Stalin when I sat where you now sit."
[I can't find the link to this just now, due to company's whitelist approach to deciding which web sites are safe]
In case anyone is interested - the actual number the UK government estimated it would take was 3, the Soviets targetted many hundreds of them.
https://www.youtube.com/watch?v=9GJttnC8PoA
In best British tradition it does even manage a bit of exceedingly dark humour.
(For those who haven't seen it, it is grim, but gripping.)
He also made Connections [2] with James Burke, which is a fantastic documentary series about the history of science.
(His later, very commercial Hollywood work is less interesting, though Steve Martin's L.A. Story is great.)