City building department head Gregor Bonin told journalists late on Tuesday experts had found falsified protocols and metal anchors that had not been installed properly at six different underground metro construction sites on the U-Bahn Wehrhahn line.

“There is criminal energy at play here,” Bonin said, adding that the city has filed charges against two people in the case.

After the March 2009 collapse of Cologne’s city archive, which killed two people and destroyed countless precious documents, officials there launched an investigation into metro construction practices that may have led to the accident. They have since uncovered systematic falsification of building protocols and evidence that construction companies were skimping on concrete and other materials.

Bonin said there were clear indications that similar incidents in Düsseldorf were perpetrated by the same people as in Cologne – employees of a company called Bilfinger Berger – and those under suspicion have been suspended from their duties.

Because no safety danger has been detected in relation to these practices, construction of the U-Bahn line will continue as planned, he said.

Meanwhile Düsseldorf Mayor Dirk Elbers said in a statement that he would insure “open and transparent” investigation into the situation.

“The Wehrhahn line will be absolutely secure,” he said.

Cities that may have worked with Bilfinger Berger on U-Bahn construction in the last 40 years have been asked to file reports.