Under Subsection (a), the court is granted rather broad authority

to modify its prior release order on a showing that such modification is needed. Subsection (b), on the other hand, is more limited in that the court must find either that there have been willful violations of his prior order or that a court or grand jury has found probable cause to believe that the person released has committed a subsequent crime while released on the pending charge. In the latter circumstances, preventive detention seems constitutionally permissible.