Some things I don't understand (Spoilers)

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Double jeopardy means that you cannot be tried for the same crime if you are found not guilty. CJ was found guilty in the first trial, but when it was shown that the DA was planting evidence, all of his cases had to be reviewed. When CJ was let out of prison, it was announced that there was probably not enough evidence to retry him. His connection with the murdered prostitute (blackmail) gave them more evidence to look at. "Taniesha" and her story were fabricated, but gave CJ his first big break in reporting. After he landed a better job, she demanded more money to keep quiet or she would ruin his career. She kept calling him in the beginning of the movie, so he hatched a plan to get rid of her, cover his tracks in the murder, and have the story he needed by exposing the crooked DA. I believe he had the tape (as well as the award) to impress Ella or any other girl he took home. He did not expect her to make a connection to the murder when only hands were shown in the video.

-"I don't really like talking about my flair"- Office Space

1) He was trying to get laid. Also, it ties the story together.
2) He was acquitted. That's not the same as being found NOT GUILTY. Which is what CJ really wanted. There would however need to be another trial. Who knows how that went?
3) He won an award for that film. The film wasn't true, she was an actor. She was trying to blackmail CJ saying that she would tell the world she was hired by CJ to make the film. CJ didn't want to risk his career and a shot at winning a pulitzer so he tried catch the DA planting evidence, kill the girl, and win a pulitzer all in one fell swoop.