Mr. Sawicki is Steve Harmon’s film club adviser. He is brought forward as a character witness for Steve, explaining all the positive things that Steve has done through his film class and how he believes that Steve is an honest person. When he testifies, he says that Steve is sincere in his depiction of the neighborhood, and as a result, he is an honest person in general.

Petrocelli, the prosecuting attorney, uses two tactics to discredit Mr. Sawicki’s testimony. The first is showing that he didn’t know where Steve was on the day of the murder,

PETROCELLI
What was he doing on the afternoon of December 22nd? Did he show you a film of that day?
SAWICKI
No, he did not.

If Sawicki is just a character witness, then it makes his testimony less powerful. Petrocelli is seeking to discredit his power as a witness by showing he doesn’t actually know Steve that well, and that he doesn’t know what happened on the day of the murder because there was no film or other story involved.

The other tactic is to show that Sawicki liked Steve, which proves that he might be blinded by his feelings instead of an objective witness. The idea that he could be blinded might mean that he would testify for the boy without really knowing what he got up to in his neighborhood. Petrocelli says,

As a matter of fact, you like him quite a bit, don’t you?

The prosecutor is working to make it seem like his testimony is all a ruse to make Steve out to be a good kid. If Sawicki likes Steve, he might also be willing to lie for Steve. Not only that but while he thinks he knows Steve through his films, Petrocelli points out that he might not know Steve, except how he acts in the classroom, which could be different than how he behaves in his neighborhood.