Felony warrants throughout the United States are normally entered into the law enforcement database NCIC.
Once this warrant is entered, law enforcement agencies are able to access the information.
IF the warrant is "Nationwide Pickup" your ex will be arrested.
If the warrant is "Statewide Pickup Only" then you may have a problem if your ex leaves the state.
My own spouse has an ex who is over $30K behind in child support. He also has a felony warrant yet remains outside the state. Nice thing is...even though he's not been arrested for the child support...he HAS spent time in the Arkansas State Prison system.
There is a silver lining in the clouds!
NOTE: Seeing your additional comment...
Contact the county of which he's residing in if you have his address there. Let them know he's there and also has an outstanding warrant for his arrest.
One thing to remember is...if he's in jail...he doesn't work! If he doesn't work then there's still no child support.
Personally, I'd just as well see them sit in jail and not consider the child support other than payment for entertainment services knowing they're sitting in jail for their wrong doing.
As for the comment about "your cooperation." Don't back down when this case goes to court. See it through! This is the problem with many "victims" in a case....they are confronted by the former relationship who tells them "Oh baby...I'll never do it again!"
I am no lawyer, but if he was with you then it is impossible for him to has assaulted that person. If you can prove that he was with you that night ether through witnesses or photos then you have a very good chance of winning the court case. If if helps any photos have a time code built into them which states the exact time and date it was taken, if you took a photo that night of him with you then you are shown to be trust worthy and the judge is more likely to believe you. Overall though I think you need to consult a lawyer! To get the court to read the text messages you need to tell them that he did not assault the girl and you have proof that he wanted nothing to do with her! Then give them the text messages as proof. On the phone is best as it will again have time codes!
I hope it all goes well at court!