GEOFF BENNETT: This week, a group of U.S. lawmakers came together in a rare show of bipartisan support to call for the immediate release of Hong Kong businessman Jimmy Lai.

Lai, who owned the once popular newspaper Apple Daily, is one of hundreds of democracy activists, journalists and political leaders imprisoned as part of mainland China's ongoing crackdown on dissent in Hong Kong.

Nick Schifrin recently spoke to his son and lawyer, who were in Washington, and are fighting to improve his conditions in prison and secure his freedom.

NICK SCHIFRIN: Jimmy Lai arrived in Hong Kong at the age of 12 stowed away on a fishing boat.

He worked his way up to become an outspoken pro-democracy advocate and media tycoon.

In the summer of 2020, he became the most prominent person arrested under a national security law that punished people not only for what they did, but also what they said.

Anyone who participated in actions that Beijing-backed courts defined as calling for separation from mainland China, who received support from a foreign country, or who -- quote -- "provoked the hatred of Beijing" could be arrested and sentenced to life in prison.

Recently, Jimmy Lai's lawyers and his son appealed to the U.N. special rapporteur on torture, saying he has been held in solitary confinement for the last 3.5 years, and that poses a grave risk to his life and to his physical and mental health.

And I am now joined by Sebastien Lai and Caoilfhionn Gallagher, head of Jimmy Lai's international legal team.

Thanks very much to both of you.

Welcome to the "News Hour."

SEBASTIEN LAI, Son of Jimmy Lai: Thanks for having us.

NICK SCHIFRIN: Sebastien Lai, let me start with you.

What's your goal of coming to Capitol Hill and doing interviews like this?

SEBASTIEN LAI: So my ultimate goal is to see my father free before he dies.

Coming to Capitol Hill, I want to bring attention to what's happening to my father, to the injustice, and to get support to put pressure on the Hong Kong government and Chinese government to see my father free, and to stop this political persecution of my father.

NICK SCHIFRIN: Caoilfhionn Gallagher, as I just said, you appealed to the U.N. special rapporteur.

Why and what do you hope she does?

CAOILFHIONN GALLAGHER, International Human Rights Lawyer, Doughty Street Chambers: So Jimmy Lai already should not be on trial.

He's on trial, essentially, for being a journalist.

It's a conspiracy to commit journalism case.

That's bad enough in itself.

But what we also now know is that, for three years, nine months, he's been held in conditions which amount to inhuman and degrading treatment, in violation of international law, and conditions which we think pose a very, very grave risk to his life and to his welfare.

He's almost 77.

He's diabetic.

He's got various underlying health conditions.

He's also been held in prolonged solitary confinement, no access to natural daylight for 23 hours, 10 minutes per day.

And he's also devout Roman Catholic being denied access to the sacrament of holy communion.

So the U.N. special rapporteur on torture has responsibility for holding China to account when it breaches international law.

And we have asked her to take urgent action before it's too late and we see this brave man die behind bars for being a journalist.

NICK SCHIFRIN: Sebastien Lai, as far as you can tell, how's your father doing?

SEBASTIEN LAI: My father is a very strong person.

I think, as a son, I always view him as that.

But his health has deteriorated a lot.

So, even though he's mentally strong and he knows he's doing the right thing, I really worry that he will pass away in prison.

My father has been campaigning for democracy for the last 30 years, and he always had a way out, as in he could always just retire, go to London.

And he decided to make the hard decision to stay in Hong Kong to campaign for what he knows is right.

And when the hammer came down, when the national security law came down, he knew that, if he left, he would open his journalists up to attacks from the government.

And so he decided to stay, to act as a shield.

And, I mean, it's something I respect him immensely for.

And it's something I wish I would have the courage to do as well if I was put in that situation, to stand with your people and to not forsake them, when you know that he could very well spend the rest of his life in prison.

NICK SCHIFRIN: Jimmy Lai is on trial for alleged sedition and alleged conspiracy to collude with foreign agents.

Do you have any doubt that he will be found guilty?

CAOILFHIONN GALLAGHER: In short, I'm afraid to say this is only going one way in the Hong Kong system and he's going to be found guilty.

He's been tried under a law which should not exist in a trial which is profoundly unfair before judges handpicked by Beijing.

He's been prosecuted for being a journalist and for his writing, raising human rights concerns with international human rights organizations and, thirdly, speaking to politicians internationally to raise concern about these issues.

Now, all of those things are values the U.S. holds dear, the international community holds dear.

He should be praised for doing those things, not turned into a criminal.

NICK SCHIFRIN: Sebastien Lai, what do you want Washington, where you are, what do you want the world to know about your father?

SEBASTIEN LAI: My father has decided very early on, 30 years ago, that there is something that is much more important than money.

Hong Kong's a financial center, so it's a lot of -- it's a driving force essentially, but he realized very early on that, look, if you didn't have freedoms, then what's the point of all of this?

I mean, look, the last 30 years wasn't smooth sailing either.

Our house was firebombed.

He's had an assassination attempt.

Someone once skinned a dog, then pinned it on our door.

My memory of my father is always of this man smiling, because he knew that, despite all of this, he was doing the right thing.

NICK SCHIFRIN: Sebastien Lai, Caoilfhionn Gallagher, thanks very much to you both.

CAOILFHIONN GALLAGHER: Thank you.

SEBASTIEN LAI: Thank you.