China just got caught spying on Taiwan's president's family on US soil

A California real-estate agent just got charged with spying on Taiwan's president's family.

And the FBI caught her at the airport, trying to fly to China.

Her name is Wanying "Heather" Zhang. She's 34. FBI agents arrested her two days ago at Los Angeles International Airport, right before she could board a flight to Shanghai.

A federal complaint, filed the day before her arrest, charges her with acting as an unregistered agent of the People's Republic of China.

Zhang lives in Irvine, California. She's a licensed real-estate agent with JC Pacific Capital.

So who was she watching? The complaint itself doesn't say. But law enforcement told CBS News the target was Ting-Yu Lai. He's the US-based son of Taiwan's president, Lai Ching-te. CBS says investigators matched surveillance images to an address near Seattle that he owns.

So this isn't a stolen-document case. This is the family of a sitting head of state being watched on American soil.

Here's how it started. Back in June last year, Zhang was introduced to a Chinese government official. The introduction came through a former classmate, from a school in Beijing called the University of International Relations. The FBI says that school has ties to China's Ministry of State Security.

That same month, Zhang travelled to China. She allegedly booked a private room in Changsha and met the official there. He gave her the surveillance job. She later messaged him that she could take care of it herself, the complaint says.

Then in August, she told him she'd be heading to Seattle the following week. He thanked her for her work, according to the complaint.

On 1 September last year, Zhang and an associate flew from Las Vegas to Seattle. Court papers only name him as "Individual 1". They rented a black Nissan Rogue. They drove to the target's home.

A neighbour's security camera allegedly caught them filming Ting-Yu Lai, his wife and their child, as the family arrived home.

Here's where it gets specific. Investigators pulled messages off Zhang's iCloud account, under a search warrant.

And in those messages, Zhang allegedly wrote to a Chinese government contact on WeChat. She says quote "Saw him. Young male. It's that young one". Then she said she was recording video. Then she sent two licence plate numbers.

A few days later, she told the associate to send the photos by AirDrop instead. Not WeChat. Not text. Her message said it had to go that way, because she had to pass it on.

The associate later told her he'd deleted the photos. He said he'd cleared them from his deleted folder too.

The FBI agent who wrote the complaint described that as an apparent attempt to destroy evidence.

So that's an FBI agent calling this evidence tampering, under oath.

Why does this matter so much? FBI Special Agent Kevin Holt wrote that information about the relatives of senior Taiwanese officials could give China's government leverage in a future conflict over Taiwan.

So this isn't espionage for secrets. It's espionage for who to threaten.

And under US law, anyone acting for a foreign government here has to tell the attorney general. Zhang never did, the complaint says.

Bill Essayli is the First Assistant US Attorney for the Central District of California. He confirmed the arrest. He says quote "coordinated the trip with an associate and used tradecraft to avoid detection". He also said Zhang is a naturalised US citizen.

Kash Patel is the FBI Director. He used this arrest to send a bigger message: that America is no longer a safe place for foreign adversaries to run espionage operations.

Zhang's husband is Edric Ding. He's also a realtor, at the same firm. He told CBS News by phone that he didn't know anything yet. He wouldn't say more.

China hasn't responded to the arrest. China's government offices are shut this week for the National Day holiday. It's still not clear if Zhang has a lawyer.

Zhang was due in federal court in Los Angeles the day after her arrest. She is presumed innocent unless proven guilty.

And this isn't the first case like it. Back in May, former Arcadia mayor Eileen Wang was charged with acting as a Chinese agent. She said she took payment to spread pro-Beijing propaganda.

So here's what nobody's said yet. Was Zhang the only one watching this family? And will the Chinese officials who allegedly directed her ever face anything at all?