I had about 170 MiB free space in my Raspberry Pi so I decided to delete the .deb packages (about 800 MiB) in
sudo pcmanfm, selected the files and pressed the delete button (not shift+delete). The files were gone, but the free space did not increase.
pcmanfm window with elevated privileges says that recycle bin is not supported, and the files did not go to ordinary recycle bin.
If the free space did not increase, then where did the files go, and how to delete them properly?
I am using latest version of Raspbian.
The deleted files were in
/root/.local/share/Trash/files/. They were found following the accepted answer.