Legal Question in Criminal Law in California

First of all the DA cannot bring "names into a trial"--only witnesses can do that. Witnesses can be cross examined as to why they think a certain person is a member of a gang.

Mr Shapiro is correct

Things that are said at trial, whether that is a civil trial or a criminal trial, are privileged and cannot be the basis of future slander or defamation suits. That privilege is set forth in Civil Code section 47. Without it, people would be reluctant to testify and our court system would grind to a halt.

The only limit on the DA is what is known as prosecutorial misconduct, which can get the deputy DA in trouble with the California State Bar when it the misconduct is excessive.