Vann's public defender put his hand on Vann's shoulder to encourage him to speak, and Sullivan warned the suspected killer he would "spend the rest of his life" in jail until the hearing happens, The Associated Press reported.
Instead of speaking, Vann stared straight ahead.
Sullivan postponed the hearing until next week.
His silence comes after he cooperated with police, confessing to seven murders and showing police where to find the bodies.
Vann helped authorities locate the bodies of six other victims, all stashed in abandoned homes in Gary, Indiana, because "he was looking for a type of deal with prosecution," Hammond Police Chief John D. Doughty said at a press conference this week.
The suspect indicated to police that his murders date back two decades, and police suggested there could be additional victims.
The Lake County coroner said today that they have identified four of the women and are seeking the public's help in identifying the remaining three. Seventeen families have called the coroner's office to make missing persons reports to see if the victims were their family members.
The coroner said at least one other woman was strangled, and the cause of death of the remaining five was not yet determined.
At least three of the victims were skeletonized by the time they were found, a process that could take between two weeks and months depending on the environment, a spokeswoman for the coroner's office said. Two of the skeletonized bodies were found together.
The office asked that anyone with information about the victims to call 219-755-3267.