I will paste my answer in this topic as well. I hope everyone who needs similar functionality will find the asnwer here.
I would suggest you to use Keyboard.Modifiers property in order to get the pressed key. For example:
if ((Keyboard.Modifiers & ModifierKeys.Control) > 0)
For more information, please refer to the following link in msdn - http://msdn.microsoft.com/en-us/library/system.windows.input.keyboard.modifiers.aspx
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