The owner of the car got it from his friend in July and the car was from (guess where) the 20-kilometer radius "no entry zone" in Fukushima Prefecture.
The 20-kilometer "no-entry zone" was officially off-limit until June and the residents weren't allowed to use their own cars until September. Unofficially, there were "rumors" (i.e. not reported in the media) during the summer that people were hired to go and retrieve vehicles inside the 20-kilometer zone. There were also "rumors" of sudden deaths among people who were doing exactly that. The existence of this car in Musashino City, Tokyo is a proof that these reports may have been true.
The car was found emitting over 30 microsieverts/hour radiation at the front grill and inside the engine room. At the perimeter of the parking lot at 1 meter high, the air radiation was 3 microsieverts/hour. Judging by the way the city crafted the announcement, their survey meter went overscale at 30 microsieverts/hour, and the actual radiation level could be much higher.
It was only on December 21 that a citizen finally alerted the city about this radioactivity on wheels.
From the announcement at the Musashino City website:
Regarding the automobile in a parking garage in Nakacho 2-chome, we were notified by a resident on December 21 of the high radioactivity. We measured the radiation level and confirmed it to be high. Therefore we did the following in response:
We confirmed the radiation, and with the help of the Musashino City Police closed off the area after securing safety.
Then we asked for guidance from the Tokyo Metropolitan government and the national government. While we waited for the answer we moved the car to the underground parking at the City Hall, and kept it there limiting the access.
We asked for assistance in decontamination from the Nuclear Disaster Response Headquarters of the Prime Minister's Office. Since the radiation from the car exceeded 30 microsieverts/hour, it was decided that it would be appropriate to return the car inside the "no entry zone" in Fukushima Prefecture.
On December 22 morning, the Prime Minister's Office and TEPCO would transport the car to Fukushima Prefecture, and conduct decontamination and radiation measurement. If the radiation would not drop below a certain level, the car would not be able to leave the "no entry zone".
The owner of the car is a city resident who says he received the car from his acquaintance in July. It has been revealed that the car was used inside the "no-entry zone" before and after the Fukushima I Nuclear Power Plant accident.
After the car was moved, the radiation levels in the vicinity were confirmed to be below the limit that the city sets (0.23 microsievert/hour).
Radiation levels (from the chart at Musashino City's website, above):
Perimeter of the parking lot at 5 centimeters off the ground: 2.60 microsieverts/hour
Perimeter of the parking lot at 1 meter off the ground: 3.08 microsieverts/hour
Car, front grill: more than 30 microsieverts/hour
Car, inside the engine room: more than 30 microsieverts/hour
7 meters from the car in both north and south directions at 1 meter off the ground: 0.19 to 0.23 microsievert/hour
After the car was removed, the radiation levels on the parking lot dropped to 0.11 microsievert/hour, post-Fukushima normal, so to speak.
It looks like there is a kindergarten within 3 minutes of walk from this particular parking lot, which costs about US$320 a month to rent a parking space. This car has been in this parking lot, and running around in town and maybe beyond, for 6 months. It would have continued to do so without the report from a citizen armed with his/her survey meter.