Where can I find statistical data on the pros and cons of illegal immigration in America & other countries?

I am looking for statistics and facts, not opinions. I need links that provide empirical data. Please do not include political statements of agenda on either side of the debate. But links that include statements by members of the senate, house of reps, or any presidents or vice presidents, past and present, could be helpful. Or even statements from a religious standpoint could help. Even facts and stats provided by studies in other countries are welcome. As long as they provide hard facts. This is not about immigration in general. Just the topic of illegal immigration. Thanks for your help.