Filegroup can't be removed

I got the following error when i try to remove the filegroups. I have remove all the files before running removing filegroups script, but still met the error.

Msg 5042, Level 16, State 12, Line 1
The filegroup '*****' cannot be removed because it is not empty.

The filegroup id is 4. And i run the script to check if the filegroup is using but nothing return.

SELECTgroupid,
       name
FROM   dbo.sysindexes
WHERE  groupid=4
ORDER  BY groupid,
          name