I was misled. What should I do?

My friend asked me to speak on behalf of her son at his sentencing in federal court. He was, to my knowledge, being sentenced for having 2 pictures of child pornography on his computer. I'd been led to believe that these could have been accidentally downloaded as a virus, or as attachments to music downloads. I went into court prepared to speak on behalf of this young man, whom I had always thought of as a model citizen. I was stunned when the prosecuter began to outline the case. Only then did I learn that there were 40 pornographic photographs of children found on the computer in question. Luckily, I didn't have to speak in the end, but what I had prepared would have been a travesty of what I actually felt after learning the truth. The young man ended up being sentenced to three years in federal prison for possession of child pornography. I had gone to his sentencing prepared to beg for leniency and to ask the judge to give him probation! I feel used and betrayed by this whole matter. Maybe his mother didn't even know the extent of his involvement in child pornography until that day in court. But what if she did, and she was keeping me in the dark? I'm confused about whether I should confront her about this. I'm mad and I'm embarrassed that I even showed up. How should I move forward with this?