About 2,000 people protested in Brussels on 19 August after several smaller demonstrations outside the convent in the town of Malonne, southeast of the capital.
Protesters have also daubed graffiti on the convent walls and posted pictures of two of the four girls who died in a makeshift dungeon Dutroux and Martin had in their house.
Brussels Archbishop André-Joseph Léonard issued a statement stressing that the nuns' offer to Martin could not undermine the bishops' determination to root out clerical sexual abuse cases and put victims' needs first.