How to identify who made a change
SQL server has "default trace" running by default.  You need to search the trace files using something like this:

--Find current trace file name
--Select * from sys.traces  

SELECT 
     loginname,
     loginsid,
     spid,
     hostname,
     applicationname,
     servername,
     databasename,
     objectName,
     e.category_id,
     cat.name as [CategoryName],
     textdata,
     starttime,
     eventclass,
     eventsubclass,--0=begin,1=commit
     e.name as EventName
FROM ::fn_trace_gettable('H:\MSSQL10_50.ODS01\MSSQL\Log\log_217.trc',0)
     INNER JOIN sys.trace_events e
          ON eventclass = trace_event_id
     INNER JOIN sys.trace_categories AS cat
          ON e.category_id = cat.category_id