HG: find where a deleted line was removed

hg log -p fileName > fileName.log

Then open the fileName.log file

In there you will find commit the details of each commit along with the diff of that commit. The details of the commit includes the username.

hg grep will let you search a change log for a pattern, such as a deleted string. If you are looking for more than just the first occurrence, be sure to include the --all flag. For me it looked something like this:

hg grep --all -r 9876:tip "pattern" path/to/file

Thanks to Anton for the helpful comments and krtek for his related answer.