"The dissecting room and the slaughter-house furnished many of my materials" (Chapter IV).
Victor informs the reader in Chapter Four that he returns to his "old habits," that is he begins to frequent the dissecting rooms again, only this time as a collector, rather than a mere observer. He also mentions gathering bones from 'charnel houses.' Unlike the 'Hollywood' versions of the novel, Frankenstein does not have an 'Igor'--a gruesome assistant searching for brains in rotting crypts.
Victor does confess to "dabbl[ing] among the unhallowed damps of the grave," but Shelley's diction here remains purposefully vague. Taken in context, Victor's graveside remark seems like figurative language, a metaphor, for his preoccupation with death and dead tissue; but upon considering Victor's fervor for completing his task, it is not totally untoward for the reader to consider that Victor may have robbed a few graves in order to complete his project. If anything, Frankenstein is a novel that reveals how Victor's obsession in the name of science superseded his morality.