The two typewriters displayed at the hearing were IBM Selectric typewriters that use elements instead of carriages for typing. They are electric typewriters. But Burger did not use them for demonstration purposes, only for display purposes, in front of enlargements of documents that had been typed on them. Thus, there was no reason for them to be plugged in to an electric outlet. Nevertheless, when Lt. Anderson was asked to type with them, no one had to plug them in.
When Perry Mason was speaking to his two clients (co-defendents) in jail, there were two guards right outside of the jail cell that Mason & his client's were in. This violates attorney/client privilege.
Perry had a police officer type a line on one of the typewriters. During the typing, a close up showed the keys striking the paper. Perry showed how easily the balls in the two typewriters could be switched. The typewriter he used in the original close up was not a ball type typewriter.
When Lt. Anderson is asked to type a few lines by Perry Mason, he only actually
types about ten or twelve characters with each typewriter and yet there are
about 75 characters in what is on the paper that comes out of the typewriter.
At 5m44s, the letter being typed by Terry Clover (secretary) to "Holmes Metals, Inc." on the letterhead of Aerospace Reliability Associates is shown in close-up on the typewriter whilst being typed: but after the single word salutation "Gentlemen:", the letter consists only of continuous lines of random characters instead of actual text.