the library achievement

To unlock the library achievement that says you gotta beat it in under 30 minutes, can this be done cooperatively or does it have to be single player?

If the achievement description doesn’t specify, then it can be done on either.

Cant find it for you if you can do it co-op but if you won’t to do single player he is a link I did this the second time http://m.youtube.com/watch?v=pzVLtJDhVJE

It doesn’t say anything about it requirements.
Go ahead and co-op!
It will be easier and quicker anyways…

Doesn’t it have to be done on veteran without dying? Good luck doing it coop…