A dozen fingerprints lifted from a folder and a notebook found at a makeshift explosives lab during the 2019 protests prompted a 19-year-old defendant to reverse his previous not guilty plea just moments before his trial was slated to begin at the District Court on Tuesday.

Student Ting Chin-fung had initially denied two explosives charges, as well as a third relating to drones believed to be intended for carrying bombs. However, Ting rescinded his plea and admitted the explosives allegations after prosecutors submitted last-minute fingerprint evidence indicating his involvement.

The court heard Ting had joined fellow student Tung Sheung-lam, 25, and other unknown conspirators in manufacturing gunpowder and thermite inside a tenement flat on Oak Street in Tai Kok Tsui in October of 2019.

Police arrested the pair at 7.30pm on October 15 after the latter was seen leaving the building.

The makeshift laboratory was being used to store 723 grams of potassium nitrate, 413 grams of carbon and 457 grams of sulphur – enough raw ingredients to produce 723 grams of gunpowder.

Investigators also found 666 grams of a mixture of powdered aluminium, iron oxide and magnesium carbonate, all common ingredients of thermite, a substance that burns at very high temperatures. However, the mixture at the lab was incapable of ignition as there were miscalculations in the ingredients’ proportions.

The flat also contained 23.5 litres of petrol, 1.3 litres of organic solvents and three drones thought to be capable of carrying small firebombs.

Tung, who rented the flat, pleaded guilty last month to conspiracy to make explosives, possession of explosives and possession of articles with the intent to damage property, charges which Ting denied.

But Ting decided to plead guilty on Tuesday after prosecutors filed an additional forensic report on a folder and notebook seized from the flat that contained diagrams of improvised weapons and notes on the anti-government movement and protest equipment.

Officers found a total of 86 finger and palm prints on the documents, about a dozen of which belonged to Ting, prosecutor Ivan Cheung Cheuk-kan said.

The prosecution agreed to drop the charge of possession of articles with intent to damage property provided that Ting admitted the other two.

Both Ting and Tung will be sentenced on September 16.

Making or possessing explosives and possessing articles with the intent to destroy or damage property are all punishable by up to seven years in jail in the District Court.