"CBP officers may, at times, inspect a person's belongings to determine whether or not items are admissible or are illegal."
Woo didn't say how a sketch of a car could trigger a border guard's suspicion of copyright infringement. But he did say agents are trained in trademark and copyright laws.
"It's a part of a CBP officer's training. Time is set aside for intellectual-property-rights training."
The agency's role is to keep the country's borders safe while at the same time enforcing many rules and regulations, he said.
"If somebody brings in artwork, it's not necessarily the artwork but (whether) it's intended for a specific use, such as a commercial nature. It doesn't mean the drawings themselves are bad, but what they'll be used for."
He said Customs and Border Protection is in more than 300 ports of entry and processes 1.5 million people a day.
"We appreciate passengers that appreciate we have a job to do. We stress that our officers are professional."
Zempel said that even as she was being questioned, the border officer "was very cheerful. She was very pleasant."
The problem, Zempel said, is "I wasn't doing anything suspicious. I was doing something unpredictable."