The Beijing Municipal Public Security Bureau said five people were in custody for the crash in which a vehicle intentionally plowed into a crowd of people in the square before bursting into flames.
Usmen Hasan, his mother and wife were inside the Jeep, which had a Xinjiang license plate, China's state-run news agency Xinhua reported.
The crash killed two tourists in the square, a woman and a man, and the family inside the Jeep died after they set gasoline on fire inside the vehicle, Xinhua said.
Monday's crash injured 40 people at the square, a spokesman for the bureau said.
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