Duisburg Mayor Adolf Sauerland and Lopavent owner Rainer Schaller, who have been implicated in previous media reports, were not among the targets of the investigation.
Potential charges against the suspects are manslaughter and negligence for their alleged part in the deaths of 21 young people crushed to death at the techno music festival on July 24, 2010.
The tragedy occurred after a massive crowd of revellers were herded through a narrow tunnel and the build-up of pressure sparked a panic that led to a deadly crush. More than 500 people were injured, many of them severely.
The city of Duisburg said it was a “normal and expected step” for its officials to be investigated, but that it would protect its employees.
Duisburg Mayor Sauerland said he would also stand behind the officials, adding that he was convinced that “we all acted according to our best knowledge and violated none of our official duties.”
Meanwhile North Rhine-Westphalia Interior Minister Ralf Jäger said those responsible for the tragedy must be investigated and prosecuted.
“But punishment alone doesn't go far enough,” he said. “It is at least as important for us to reach the right conclusions from the Love Parade for large events in the future.”
In the six months since the accident prosecutors and police have interviewed more than 2,200 witnesses, along with reviewing thousands of photos and surveillance videos.
A spokesperson said he could not rule out the investigation of further suspects as the their probe continues.