The difference between police killings in the United States and Chinese internment of Uighurs is that for the former it is very widely documented by American newspapers and databases. The US has a free press that can criticise American policies including the violence of police departments.
China does not allow a free press. With the camps other media has to make educated guesses how many are in the camps. They also haven’t given an estimate of how many Uighurs are in camps. This is extremely important because it shows they are not looking to refute the allegations.
1.3 million went to Xinjiang “vocational training centres” during 2014-2019 https://www.scmp.com/news/china/politics/article/3101986/china-claims-vocational-training-given-nearly-13-million-people
An AFP study found out that the vocational education bureau in Hotan County ordered 194,000 Chinese language practice books and 11,310 pairs of shoes. https://www.afp.com/en/inside-chinas-internment-camps-tear-gas-tasers-and-textbooks
BBC analysed satellite images and found out that 44 of them had the potential to be re-education camps. One of the camps in Dabancheng had the potential to house at least 11,000 detainees and at most 130,000 detainees. The low estimate assumes that each person has his/her own room, and the high estimate assumes that there are dormitories instead of individual rooms
https://www.bbc.co.uk/news/resources/idt-sh/China_hidden_camps