FORT LAUDERDALE — Claudette and Major Melvin spent their last days doing what grandparents do: Doting on their children and grandchildren, going to church and spending time with one another in the quiet corner home in Melrose Park, surrounded by trees. Then violence entered their lives, seemingly at random.

Twelve days have passed since the 85-year-old and 89-year-old were found shot to death in the Fort Lauderdale home where they have lived for more than 40 years. Still, police have not made any arrests or found the couple’s red car that might hold the key to solving the case.

At a Wednesday news conference, Fort Lauderdale Homicide Detective Sgt. Donald Geiger and lead Homicide Detective Leann Swisher joined the couple’s youngest…