Why is the subjunctive used in this sentence?

I was reading this article in spanish and was confused about the imperfect subjunctive being used here, because they are talking about a fact.

…despues de que EU matara en Bagdad al poderoso comandante iraní Qasem Soleimaní en enero de 2020.

Is it because they're implying that this isn't a fact? That it's not 100% confirmed that the US killed Qasem Soleimani?

It's probably just an incomplete understanding of the subjunctive on my part. Thanks for the help!