Why not try them first?
In absentia?
"Occasionally a criminal trial is conducted without the defendant being present when he/she walks out or escapes after the trial has begun, since the accused has thus waived the Constitutional right to face one's accusers."
Before "Kidnapping" someone, you would assume that the federal prosecutors have overwhelming evidence ensuring a conviction.
After such a conviction, the person becomes a fugitive and the act of nabbing the bad guy becomes "Bounty Hunting" not "Kidnapping"
?