Items on external hard drive not erasing.

I have a friend that I just got to convert to a Mac user. He has a 1Tb Seagate Go Flex HD. He moved a few files into the trash and when he tries to empty his trash it will not empty. Now when he ejects his hard drive the file are no longer in the trash but when he plugs it back up the come back. I tried Super Empty Trash and it will not do it either. He had right at 900Gb of stuff on it he does not want to lose. Any help would be appreciated.

I'm guessing that it may have to do with the permissions on the files being read only on the drive, as it is formatted NTFS for his windows PC.