Deleting file in /tmp directory

Hi, I have this PHP script (simplificated here), called delete_tmp.php that basically calls external commands: <?php $session_file = '/tmp/sess_89765' system(''rm -f' . ' ' . $session_file); ?> delete_tmp.php file is owned by gamito.users /tmp/sess_89765 file has permissions -rw------ and is owned by gamito.users My /tmp permissions are rwxrwxrwt and is owned by root.root I know that the the sticky bit only allows files to be deleted by their owners, the owner of the directory or by root. Never the less, i can switch to /tmp directory and delete sess_89765 file as user gamito. If I run: $ php delete_tmp.php as root, it deletes sess_89765 file. But if I do the same has user gamito, it doesn't delete the file !!! Ideas ? Any help would be appreciated. Warm Regards, Mário Gamito