Complex sentence: Since the start of the protests tens of thousands of people have been holding day-and-night vigils at Shahbag, refusing to leave until all those convicted of war crimes are sentenced to capital punishment.
Split into simpler sentences: Since the start of protests, tens of thousands of people have been holding day-and-night vigils at Shahbag. They say they refuse to leave until all those convicted of war crimes are sentenced to capital punishment.