From Longman Dictionary of Contemporary Englishfor all I knowfor all I knowNOT KNOWused to emphasize that you do not know something and say that it is not important to youI don’t know where she is. She could have been kidnapped for all I know. →know
Examples from the Corpus
for all I know• It cost millions. It could be billions for all I know.• And they probably have cameras on it for all I know.• During the war for all I know?• He might even be her source, for all I knew.• There were a few people around, polishing and sweeping, and maybe spreadingincensefor all I knew.• You might be from the newspapers, for all I know.• The reallosers will, for all I know, eat dirt.• I opened the window, and for all I know it's still open.• Snow and ice were deadlyfor all I knew, never having driven on either.