Finder shows .dmg is unmounted, Trash refuses to delete it I downloaded a .dmg file for an application, and now after installing the app and unmounting the .dmg I can't delete the .dmg file because Trash says it's "in use". Finder shows no mounted .dmgs, yet if I use the lsof command in Terminal and filter for the filename it shows that a process called diskimage is using it. What do I do?

I should mention that when I initially downloaded the .dmg file to Downloads and tried to open it from there, nothing happened. I clicked it several times and got nothing. My browser was writing a bunch of temporary files to Downloads (I was using an extension to download a bunch of files at once, that was the source of that), so I figured that folder was "busy" and moved the .dmg file to another folder. Sure enough clicking on it from there finally got it to mount. I'm wondering if all that clicking with nothing happening earlier actually mounted a bunch of disk images that for some reason are hidden. Could that be possible? Also, I ultimately ended up junking the installed application, but I don't see how that could be a factor.

I am using OS X 10.6.8.
Rebooting should clear all the processes that are using the file and unmount all potentially mounted disk images. Once rebooted, try deleting it again.