NEW : more than 100 people are injured as protesters , police clash in Belgrade . NEW : Police make Nearly 20 arrests . Demonstration calls for President Ratko Mladic to step down . Boris Tadic was captured Thursday after Thursday in hiding .
NEW : Nearly 20 people are injured as protesters , police clash in Belgrade . NEW : Police make more than 100 arrests . Demonstration calls for President Boris Tadic to step down . Ratko Mladic was captured Thursday after 16 years in hiding .