Charles Nagel, 36, from Philadelphia, Pennsylvania, was charged with federal interstate stalking earlier this year (10) for allegedly bombarding the Law & Order: Criminal Intent star with creepy love letters and turning up at the set of her hit TV show in New York.
He is also accused of sending messages to Erbe's brother and her 14-year-old daughter on Facebook.com in a bid to contact the actress.
Nagel, who denies the charge, went on trial this week (beg01Nov10) in New York City and Erbe's ex-husband Kinney took the stand at Brooklyn Federal Court on Tuesday (02Nov10) to testify.
He told the court his daughter became hysterical when she allegedly received a long, rambling internet message from Nagel.
Kinney said, "She was screaming and she was crying. She was holding her computer out in front of her saying, 'It's him! It's the guy!'"
Erbe's brother Jonathan also testified that he was "terrified" when he allegedly received a message from Nagel, adding: "I was afraid for my sister."
Erbe is due to take the stand on Wednesday (03Nov10), according to the New York Daily News.