Judge Michael Russo said the 90-day speedy trial requirement could be waived if more time is needed to prepare for trial, WKYC-TV, Cleveland, reported.
Cuyahoga County Prosecutor Timothy J. McGinty told the judge he plans to present additional evidence to a grand jury and expects to file new charges, The (Cleveland) Plain Dealer reported.
The 329-count indictment against Castro covers only the period between August 2002 and February 2007.
Castro, 52, is accused of kidnapping Amanda Berry, Gina DeJesus and Michelle Knight between 2002 and 2004 and holding them hostage in his home until they were freed in early May.
Castro is charged with two counts of aggravated murder in connection with two alleged forced abortions, 139 counts of rape, 177 counts of kidnapping, seven counts of gross sexual imposition, three counts of felonious assault and one count of possessing criminal tools.
He pleaded not guilty last week.
One of Castro's defense attorneys said last week Castro was willing to plead to some of the charges if he were spared the death penalty. The attorneys said Wednesday the prosecutor had not responded to their offer.
Russo set the next pretrial hearing for June 26.