The 12 activists aged from 16 to 33, were all facing charges related to last year's protests and one had recently been arrested under the new National Security Law.
They had set off in a speedboat from Po Toi O harbour on Hong Kong island, hoping to reach Taiwan and seek political asylum.
They made it just 45 miles when they were spotted and arrested by the Chinese Coastguard.
They are now being held, indefinitely, in a detention centre called the Yantian Jailhouse, in Shenzhen. It is on the mainland, just a few miles across the border from Hong Kong.
In order to protect themselves and their relative being held in Chinese custody, the family of one of those being held agreed to talk to us in Hong Kong. They too are being monitored by police.
They told us they haven’t heard anything from him since he left four weeks ago.
They tried to hire a lawyer for him but they were not allowed access.
Other families were told that the Chinese Government has appointed lawyers for all of the group, but nobody has heard anything from them. They have no idea what kind of conditions they are being held in and what charges they might face.
The longer they go without information the worse they fear.
It was an extradition bill and the prospect of prison in China which sparked the recent unrest in Hong Kong. The country’s legal system is notoriously opaque, suspects can be held for years without trial and inhumane interrogation techniques are commonly used.
China has confirmed they are being held in criminal detention and the group has been labelled ‘separatists’ which indicates that they will be facing the most severe of charges, and harshest of penalties.
They will almost certainly be charged with illegal border crossing and then likely face the additional charges under the National Security Law - succession carrying a maximum life sentence.
We spoke to a lawyer who is trying to represent one of those held in Shenzhen and they told us that the group can be held for 37 days before they are officially arrested and then it will be at least two months, but likely many more, before specific charges are detailed.
The group had made a pact to keep their plan secret so none of their families knew or had the opportunity to try to dissuade them from their attempt to escape.
One of the relatives we spoke to remembers her loved one giving her a very fond farewell and saying how much he loved her, on what she now knows, was last time she will see him in several months - if not years.