What city where you in? Usually it goes to salt county if the city doesn't have an established animal shelter. Look up in Google maps what animal shelter is closest to you. You can call as well, to ask staff members if their facility is the right place to report the abuse. Thank you for being a good samaritan, not many people left in this world like you.
You should have called the police.
It doesn't matter where either of you are from. He committed a crime. Call the police and give them his license plate number and a report. If possible go and ask other people who might have seen this to give a statement to the police as well. More witnesses = more action.
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