Interpol has been called in to investigate shipment of 2,000 bottles of hydrogen peroxide to the territory from Canada by the controversial Church of Zion.
The move came after a police dossier passed to the Legal Department was returned to detectives stamped 'more investigation required'.
Yesterday, officers from New Territories North Regional Crime Unit said initial legal advice, issued late last week, had prompted a shift in the focus of the six weeks' investigation.
The joint police and Health Department inquiry will now centre on the consignment of hydrogen peroxide shipped to the territory earlier this year.
The Church of Zion has confirmed two separate shipments of 1,000 bottles were received through its Canadian sister church between May and June.
But it insists the shipmentwas legal and the church only 'facilitated their delivery'.
'We simply made it possible for individual members to order and receive the hydrogen peroxide. We did not advertise it,' said Zion Mongkok cell group leader Li Pak-hon.
New Territories North Regional Crime Unit Senior Inspector Chan Lok-wing said: 'We have contacted Interpol and we hope to glean some information on the shipment from the Canadian end. We are also working with the Health Department.
'We are still looking at possible breaches of advertising laws and offences under the Pharmacies and Poisons Ordinance.' A spokesman for the Trade Department, which is responsible for issuing import licences, said hydrogen peroxide did not require a licence. Problems would only arise if it was being imported for medical use.