German authorities have been in a state of shock after a van "crashed" into people drinking outside a bar in the city of Muenster, killing two people and injuring 20 others.
Inside the apartment where the man was living, which was near the crash scene, police found more firecrackers and a "no-longer usable AK-47 machine gun".
Der Spiegel reported that police were investigating a similar incident that occurred in the eastern German city of Cottbus on Friday evening, when a man drove his auto into a group of people, injuring two, before fleeing.
The driver committed suicide inside the van, police said.
Authorities have not identified the injured in the crash Saturday in the western German city but a German security official says people from The Netherlands are among them.
The 48-year-old German man, believed to be the sole perpetrator in Saturday's attack, has been identified as Jens R, who was reportedly an industrial designer. "It is one of the most peaceful cities I know", he said.
Police quickly evacuated the area and ambulances, firefighters and helicopters rushed to the scene to aid the injured.
Two of those injured were Dutch, including one in a critical condition.
Reul added: "we are investigating in all directions".
Police and prosecutors said because of the Muenster attack, they made a decision to mount raids on the suspects who are aged between 18 and 21.
German daily Die Welt reports that police think the foiled plot involved attacking spectators and participants at Sunday's race with knives.
Police tweeted that residents should "avoid the area near the Kiepenkerl pub" in the city's historic downtown area where a large-scale police operation was underway.
Local police said they were on the scene and emergency services were attending to the injured.
German news agency dpa reported that police confirmed arrests in connection with the half-marathon but gave no further details.
Armed Police officers are seen at the scene when several people were killed and injured when a vehicle ploughed into pedestrians in Muenster, western Germany on April 7, 2018. Jan Schoessler, who was among those in line, said dozens of people were waiting shortly after doors opened at 7 p.m. It says on Twitter "we thank you for your overwhelming support".
Muenster is a popular tourist destination with 300,000 inhabitants, known for its medieval old town, which was rebuilt after the massive destruction during World War II. TV footage showed a narrow street sealed off Saturday with red-and-white police tape.