The investigators believe the vinegar was stored in two plastic barrels that previously stored toxic antifreeze, the official Xinhua News Agency reported today.
However, authorities are still testing to confirm the source of the poisoning, said the news source.
The mass poisoning, which killed atleast one six-year-old child, occured last Saturday in China's far western region of Xinjiang in a village close to Hotan city.
The victims were Muslims who were sharing a communal Ramadan meal.
The case is the latest in a series of food safety scandals to hit the country over the last few years.
Leaders have been struggling to control the food sector despite introducing tough measures to crack down on the problem.
Melamine-tainted milk has continued to appear in the Chinese dairy supply chain. In 2008, milk powder laced with the industrial chemical melamine killed at least six children and sickened 300,000.
Melamine is added to milk products to artificially increase protein levels and disguise watered down merchandise.
Associated Press said revenge attacks using rat poison or other chemicals are also common in China, where access to firearms and other deadly weapons are tightly controlled.
Earlier in the month, nitrate tainted milk produced near Pingliang city killed three children and 35 others were taken to hospital.
An investigation showed that a local dairy farmer had put the poison into their competitor's milk supply, said reports.
Accidental contamination is also a problem, due to low hygiene standards, particularly in rural areas, and weak quality control by regulators.
Earlier this year, Liana Giorgi, one of the authors of a recent paper published in Food Policy on the Chinese melamine milk scandal, gave her views to this publication on why food safety scares keep reemerging in China and what needs to be done to reform the industry.
Giorgi said the focus now is on testing the end product and needs to shift to the development of quality assurance systems. She added that better understanding and supervision of the entire supply chain is also needed. To listen to her views in a podcast, please click here.