Over the past eight months, bookseller Lam Wing Kee was interrogated 30 to 40 times by Chinese agents. Each session lasted about half an hour.
In the end, the grilling zeroed in on this: Who were the sources that provided the material for the anti-Xi Jinping books that sold so well among mainlanders?
Mr Lam said the Chinese authorities' pursuing of the Causeway Bay Books booksellers - even, as many believe, at the cost of discrediting the "one country, two systems" formula - was likely driven by this goal.
"What they (the Chinese authorities) really wanted to know is, who gave the information for those books," he said in an interview with The Straits Times yesterday.
The crackdown on the booksellers has come at a time when Chinese President Xi Jinping is working to cement his power, including over rivals and vested interests.
HIS GIRLFRIEND FROM SHENZHEN
That is not what she would have wanted to say. Do you know what's the situation she is in now? She is in the same situation as Lee Bo and the rest. The other three have had the chance to return to Hong Kong, but she doesn't. I feel guilty to have gotten her involved.
BOOKSELLER LAM WING KEE, on his 37-year-old girlfriend from Shenzhen, who he said he had intended to marry and who had accused him of lying to her about the legality of the books.
LEE BO'S DENIAL
I met him at his office twice; the first time was on June 15. On both occasions he mentioned it. I remember him saying 'two people kidnapped me to the mainland'. But he did not say where he was kidnapped and how many people were involved. But I remember very clearly he mentioned it on both occasions. I was concerned and asked him about it.
MR LAM, on Mr Lee Bo denying his claims that he, Mr Lee, was taken out of Hong Kong against his will.
There's a market in China for such books. Since the launch of China's Individual Visit Scheme in July 2003, the mainland visitors have helped to revive the market for such books. If we don't sell them, we'll lose out a lot. About 70 per cent of our customers are from the mainland.
MR LAM, on how mainland Chinese tourists helped to revive his books business.
The books sold by the store did not aid in this mission. Some contained steamy gossip about Chinese leaders' private lives; others purported to offer inside information about the internal power dynamics within the leadership. Most have been characterised as delivering a mix of truth and exaggeration.
Some observers believe some of the information may have been leaked by high-placed sources looking to damage the image of Mr Xi, who has been waging a nationwide anti-graft campaign.
"The books contained very politically sensitive content; they were an invasion of the privacy of the Chinese leaders, who could be split by factions," acknowledged Mr Lam, who is being investigated by China for mailing the banned books to customers on the mainland.
He added that increased book sales in recent years could also have galvanised the authorities into actions that have angered Hong Kongers - alleged extralegal abductions including in Hong Kong itself, lengthy detention and coerced confessions from the five booksellers.
Three years ago, Mr Lam began mailing books to customers on the mainland. A year later, he sold Causeway Books, which he founded in 1993, to Mighty Currents, the publishing firm owned by Mr Lee Bo. Since then, more books unflattering to Mr Xi, who took power in 2012, have been published and sold.
"Perhaps our sales volume has also increased too significantly in recent years, resulting in adverse effects on the mainland," said Mr Lam. "With increased demand, some people have also been smuggling our books to the mainland."
On average, the bookstore sent about 15 packages to the mainland every week. Each package contained about eight books. In a year, that added up to about 5,800 books.
While the figure may be insignificant given the 1.3 billion people in China, Mr Lam believes the Chinese authorities were looking to rout out those behind the books.
He denied having any contact with the books' authors and said he only ran the bookstore.
Asked if it was true that Mighty Currents was planning a book titled Mr Xi And His Lovers, Mr Lam claimed he was unaware of it.
In the interview at the Democratic Party's office at the Legislative Council, the 61-year-old appeared relaxed as he recounted the details of what at times seemed more like an espionage thriller.
Last year, Mr Lam and four associates went missing, only to resurface later in televised confessions from the mainland.
Mr Lam returned to Hong Kong last week accompanied by two agents and on condition that he return to the mainland last Thursday, with a hard disk of the store's customer database.
The threat hanging over his head: His 37-year-old mainland girlfriend also being held by the authorities.
But he decided to stay on and held a press conference where he told reporters about the abductions and "rehearsed" confessions.
"I was so afraid to return to the mainland," said Mr Lam, who changed his mind upon reaching Kowloon Tong where he was supposed to take a train to Shenzhen.
He did not get on and instead destroyed the mobile phone he used to communicate with the agents .
Mr Lam said he is currently staying with a relative and did not see the need to seek politial asylum as he feels "safe in Hong Kong".
But he hopes the Chinese and Hong Kong government will address the issue soon so that he can move on with his life.
WATCH THE VIDEO
The interview with Hong Kong bookseller Lam Wing Kee http://str.sg/4UKu