The murder weapon is a Thompson Contender. It is a single shot weapon which does not eject its cartridge. During the episode, the cartridge is introduced as evidence in the trial, which would have been very unlikely. Later in a scene the gun is used by an assassin with rapid fire, which isn't possible with this weapon.
Mr. Mason starts examining Mr. Griswold as a hostile witness, in an effort to challenge his alibi. In the middle of his examination, Mr. Mason lets his junior colleague, Mr. Malansky, continue the examination and introduce certain contrary evidence. Then Mr. Mason forcefully resumes his examination to impeach the witness' statement about being home at a certain hour. In actual court proceedings, whichever member of a multi-counsel team opens with a witness, that attorney alone continues with that witness until said witness is excused. Furthermore, should the team recall the witness, the original team member, and only the original team member, may examine the witness at that next time.
The aperture on the end of the silencer of the murder weapon is not wide enough to allow passage of the bullet.
The gun used for the murders does not have crosshairs in the scope, which would make it difficult to aim.