Question: Help with looking at mutations from RNA-SEQ data

[ms3389]

I have RNASEQ data from from cells that have underwent a knockout treatment using CRISPR-CAS9. I've aligned the data using RUM and did differential expression analysis. Now I want to look at off-target mutations caused by CRISPR. Basically I want to compare the sequences of cells from before and after CRISPR. Any suggestions on how would I go about doing this?

Thank you.