The Cousins by Blood trailer opens with a voice recounting a police interrogation in which a detective laid out the prosecution's theory and asked why a credible blonde witness would fabricate a story. A narrator establishes the basic facts: a double homicide in Dallas in 2000, a convicted man named Ivan Cantu on death row, and a family divided — one side supporting Ivan and the other hoping for his execution. A voice connected to Ivan's defense argues that the physical evidence linking him to the crime may have been planted by others attempting to frame him. The trailer introduces Frank as a potential alternative suspect whose alibi — driving to Sherman to do laundry despite having a washer and dryer at home — went unquestioned by police. The case is characterised as fundamentally a credibility contest between Ivan and his ex-girlfriend Amy, who says she witnessed him with a gun. Other voices dispute Amy's credibility, noting she never appeared scared of Ivan and could have left at any time. Host Matt Duff identifies himself as a private investigator and frames the series as an episode-by-episode unfolding investigation. The trailer concludes with the central question: did Ivan really commit the murders, and if not, who did?
