1. I estimate that the legal basis for the Public Security Bureau to punish your classmate is as follows:

Article 2 of the Law of People's Republic of China (PRC) on Public Security Administration Punishment disturbs public order, endangers public safety, infringes on personal rights and property rights, hinders social management, and is socially harmful. If it constitutes a crime in accordance with the provisions of the Criminal Law of People's Republic of China (PRC), criminal responsibility shall be investigated according to law; If it is not serious enough for criminal punishment, the public security organ shall impose administrative penalties for public security in accordance with this law.

Article 49 Whoever steals, swindles, robs, robs, extorts or intentionally damages public or private property shall be detained for not less than five days but not more than ten days, and may also be fined not more than 500 yuan; If the circumstances are serious, he shall be detained for more than 10 and less than 15, and may also be fined less than 1000 yuan.

2, generally does not constitute a criminal offence is not included in the file. However, the punishment of the school may be recorded in the file, and it should be possible to find a relationship before graduation.

The key now is that your classmate made a statement in the public security organ. Moreover, because there is not enough criminal punishment, the administrative punishment has ended. So now I don't think it makes sense for you to change this or not.

It is hard to say whether the school will punish the students again according to the results of the public security organs. If you are really worried, you can ask your classmates to find a lawyer to file an administrative reconsideration or administrative lawsuit with the public security organ, but it should be noted that this road is not easy. Time, money and energy are beyond the reach of a student at school.

In short, it is suggested to work hard at school.