About 70 people have died after receiving treatment at a German cancer clinic where authorities were investigating three deaths already linked to the center earlier this month.

Central European News (CEN) reported that investigators are trying to determine whether cancer or a controversial substance called Bromopyruvic acid caused the deaths at the western German clinic, which is located near the border of Belgium and the Netherlands,and specializes in alternative therapy. Some holistic cancer treatment proponents believe the acid can eradicate cancer cells, but other doctors argue it’s “highly poisonous” and “not fully researched,” the news website reported.

Klaus Ross, a medical appliance seller and technician, ran the clinic. He was schooled as an alternative biological doctor and recruited patients who were told conventional medicine wouldn’t help them beat cancer. Ross also had a license to administer injections and intravenous therapy, CEN reported.

Investigators suspected something may be amiss when they received notice of three deaths and two hospitalizations that occurred between July 25 and 27 after those individuals visited the Brueggen clinic. More families came forward, bringing the suspected deaths linked with the clinic to 70. Most of the bodies would need to be dug up for analysis, CEN reported.

Ross’ list of services included cancer and pain-reducing therapy, as well as drug addiction treatment. He charged about 10,000 Euros, or more than $11,300, for a 10-week course of treatment.

