A former chief of the South Korean unit of Oxy Reckitt Benckiser was summoned by Seoul prosecutors Tuesday to face questioning over suspicions that the British firm manufactured humidifier sterilizers that resulted in numerous deaths and illnesses.

The summons came five years after the government confirmed there is a connection between people who died of lung problems and the chemicals used to clean household humidifiers. 

Former CEO Shin Hyun-woo showed up at the Seoul Central District Prosecutors' Office in southern Seoul as a suspect in the snowballing case that could have led to the death of some 104 people, including some pregnant women, since 2011.

"I sincerely apologize to the families of the victims," Shin told reporters before entering the office. 

The former CEO, however, denied that he had been previously aware of the toxicity of the products.

Shin is considered the key figure in the ongoing investigation as he headed the company between 2001 and 2005. The sterilizers in question began reaching the local market in 2001.

Two other former Oxy officials, including a head researcher, were also called in by the prosecutors to face questioning over the toxic chemicals.

The prosecution alleges that the two chemicals used in the products -- PHMG Phosphate and PGH -- were responsible for severe illnesses and deaths. Two other chemicals used were PHMG hydrochloride and MIT/CMIT, which the prosecution found not as harmful as the other two.

Companies that made and sold the sterilizers in question include market leader in sales of the disinfectant Oxy along with Lotte Mart and Homeplus, two of South Korea's largest retailers.

The humidifier disinfectant case, one of the worst scandals involving consumer products using chemicals, came to light after four pregnant women died of lung problems for unknown reasons in 2011. (Yonhap)