If you never changed the title into you or your ex-wifes name.
You will need to go back to the co-worker, get a certified copy of the death certificate.
Your Co-worker will probably have to accompany you to the DMV. With that info they should be able to straighten it out.
Oh, And bring money. They will be looking for that.
If you transferred into the ex-wifes name....Try Flowers