can't delete iphoto library
hey all, I'm using mojave 10.14.2 on iMac. I'm cleaning it up and moved my photos and iMovie libraries to external HD. All fine. But, I still had old iPhotos library that was (is) taking up 250GB, and I want it gone now that I have everything on Photos which is on ext HD (and backed up on another HD). I moved the iPhotos library to trash, but trash won't let me delete. Says it's still in use. I restarted computer (several times)/ with no other apps running it still gives me same message. It lets me delete everything else but the iPhotos library.
Any advice?
Thanks