The exotic lamp in the corner of Mosca's cell is giving off a 60 cycle hum that is being picked up by the mics.
The jury is supposed to be unsequestered, anonymous and protected from being identified, yet they are shown being driven around, walking here and there, being easily tailed to their homes, etc.
The prosecutor and Crocket speak with a frightened witness in a DA office. On the whiteboard is a list of witness names, half of which are scratched off. This means that the witness knows who else is supposed to testify and he can see that half have backed away. Not only does this frighten the witness away, but it lets him know to contact the other witnesses and to scare them off as well.