I would like to check the FTP logs first.
FTP log file name : ftp.domain.com-ftp_logcd /usr/local/apache/domlogs/USERNAME/
To check the files uploaded you can grep /var/log/messages
grep -irl USERNAME /var/log/messages
FTP log file name : ftp.domain.com-ftp_logcd /usr/local/apache/domlogs/USERNAME/
grep -irl USERNAME /var/log/messages