We will be able to send criminals home
This becomes harder outside of the EU.
Result: Bad
Within the EU, we have processes in place to return criminals to their country of origin.
It has been argued that the EU prevented the UK sending Abu Hamza to the US, which happened on the 5th October 2012. The 2 year delay on the extradition to the United States was due to a temporarily block (8th July 2010), because the UK is a signatory to the European Convention on Human Rights; where the court needed to be satisfied that he would not be treated inhumanely.
If you disagree, or would like to add more details, please let me know.
You can suggest a reason for leaving the EU, or look at the other reasons.