Judge Jon Blue in New Haven made the decision in the case of Joshua Komisarjevsky, the second man charged in the three 2007 killings, The Hartford Courant reports.
Jury selection started Wednesday, but testimony is not scheduled to begin until Sept. 19.
In contrast, the witness list in last year's trial of co-defendant Steven Hayes was released when jury selection began. Hayes is now on death row.
Komisarjevsky's attorneys requested the sealing to protect the safety of witnesses. Some witnesses in the Hayes case were harassed.
Jury candidates will see the list so they can spot possible conflicts of interest.
Komisarjevsky, 30, is accused of killing Jennifer Hawke-Petit and her daughters, Hayley and Michaela, in their Cheshire home on July 23, 2007. Hawke-Petit was raped and strangled. The girls were tied to their beds and died of smoke inhalation in a fire set by the intruders. Dr. William Petit survived.