In a statement, Pertubuhan Pelindung Khazanah Alam (Peka) said the decision not to call in an expert witness and present technical evidence “reflected gross incompetence and a lack of diligence”.

“Their lackadaisical attitude effectively sabotaged the pursuit of justice for one of Malaysia’s worst environmental crimes.

“Such prosecutorial negligence has not only betrayed public trust but also emboldened polluters who now believe they can poison rivers with impunity,” it said, adding that the case underscored systemic failures in enforcement, prosecution, and industrial compliance.

On Tuesday, the Shah Alam High Court upheld the acquittals of four company directors and the manager of a heavy machinery workshop charged with polluting Sungai Gong in Rawang, Selangor, by dumping hazardous materials into the river five years ago.

Sessions court judge Nor Rajiah Mat Zin had cleared the directors of Yip Chee Seng & Sons Sdn Bhd – brothers Yip Kok Wai, 58, Yip Kok Mun, 63, Yip Kok Kuin, 55, and Yip Kok Weng, 65 – and company manager Ho Voon Leong, 64, of the charges in January.

High Court judge Justice Hazlina Hussain said she agreed with the findings of the Selayang sessions court, which ruled that the prosecution had failed to establish a prima facie case.

Hazlina said the prosecution failed to call officers from the chemistry department and environment department to provide evidence, and that the evidence “was only presented through an investigating officer who had no expertise in preparing case reports”.

When contacted, Peka president Rajesh Nagarajan, a lawyer, said the failure to call in an expert witness was “completely unacceptable”.

He said the omission by the AGC, who was entrusted with representing the interests of all Malaysians, was a dereliction of duty.

“Heads must roll. The attorney-general must apologise to the Malaysian public for this negligence and ensure that justice is served,” he said, adding that he would raise the matter at the Bar Council’s next annual general meeting.