I attempted to delete LibreOffice from my mac and put it in the trash, but it said that it was unable to delete it.
Please also state the version of OSX you are using.
Is it possible that LibreOffice is still running? Do you have enough privileges to delete the file?
If you’re not sure if LO is still running, you can try restarting your computer, and then delete the file first (before opening any new documents, etc…)
It might be useful to note that under OSX Lion this seems to be a problem while emptying the trash for a lot of files (pdf, png, …), even if the file is not opened/running any more. Restarting the computer helps in this case.