In recent years, police and prosecutors have implemented social media in a host of new ways to investigate and prosecute crimes. Social media, after all, contains a wealth of information—and misinformation—on individual users and their networks and few laws restrict what law enforcement can do with social media data. As more social media evidence factors in criminal cases, new opportunities to solve crime and bring those responsible to justice emerge, along with questions about the fairness and reliability of such evidence. Social justice activists and victim advocates worry that social media content is being used against vulnerable groups, furthering the vilification and stigmatization of already marginalized individuals. In this piece, we discuss research on social media and the law in two types of criminal cases—gang cases and sexual assault cases—to highlight key issues at play in this digital turn in the criminal justice system. We also explore grievances within the legal field from public defenders concerned that social media companies have aligned with prosecutors and shut them out, thus placing them and their clients at a disadvantage in what is already an unbalanced playing field. These contexts point to the double-edged sword of social media use in criminal cases as it opens once-closed communication channels around criminal activity while functioning to support age-old stereotypes and disparities in court.