"I will destroy him," Richard Andrew Sniffen quoted Driscoll as telling him, adding that she repeatedly said she would take Busch down.
The testimony by Sniffen, a Christian musician and self-described music minister who performs at NASCAR outreach events, came in a court hearing in which Driscoll is seeking a no-contact order against Busch.
Driscoll says Busch assaulted her in his motorhome at Dover International Speedway in September, grabbing her by the throat and slamming her head into a wall three times.
Busch and his attorneys have denied the allegations, which are the subject of a separate criminal investigation. They have tried to portray Driscoll as a scorned woman out to destroy his career.
Busch finished testifying Tuesday morning under cross-examination from Driscoll's attorney, Carolyn McNeice, who asked a series of questions, though few of them dealt directly with the alleged assault.
As he has in previous testimony, Busch maintained that he believes Driscoll's repeated assertions to him that she is a trained assassin who often takes part in covert missions in Central and South American and Africa. He recalled one time when she left in camouflage gear and returned wearing a trenchcoat over a blood-spattered evening gown.
"Everybody on the outside can tell me I'm crazy, but I lived on the inside and saw it firsthand," Busch said when his attorney, Rusty Hardin, questioned why he still believed Driscoll is a hired killer.
Hardin later asked what Busch might have been thinking on the night of the alleged assault about hurting Driscoll.
"Frankly, that I would have got my ass handed to me," Busch said.
Sniffen, meanwhile, said Driscoll contacted him on the night of the alleged assault and told him that Busch had pushed her and that she hit her head.
"She was upset. She was angry. She was brokenhearted," Sniffen said, adding that Driscoll never mentioned having her head slammed into the wall three times. He also said Driscoll has never told him that she is afraid of Busch.
Immediately after the incident, Driscoll seemed brokenhearted and intent on seeking "reconciliation," Sniffen said. But her attitude seemed to change over the days and weeks leading to the assault allegation being made public.
Sniffen said Driscoll went "from a broken heart looking for love and reconciliation to anger and a little bit of revenge."
"She was almost embracing the fact that there was no going back," he said, adding that Driscoll told him that Busch "was not going to walk away from me."
Busch testified Monday that he decided to end his relationship after last fall's New Hampshire race, one week before the Dover race, because she was monopolizing his schedule and he needed to focus on racing.
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