China is set to pass a landmark criminal procedure law to provide more rights to detainees, including rendering all evidence collected under torture unusable, granting suspects immediate access to a lawyer, and obliging authorities to tell families within 24 hours of a relative's detention.

But for those held in China's so-called 'black jails' - secret detention centres where people are kept without charge and without having been formally arrested - what is written in law can be very different to what happens on the ground.

Melissa Chan joins relatives of the missing seeking answers about their family members at one such facility in Beijing in this Al Jazeera exclusive.