How does accessnow figured out that pegasus spyware infected serval iPhones in jordan?

so basically I'm curios to learn and understand how did accessnow figured out whether an iPhone is indeed infected by pegasus spyware or not


source to the article:


https://www.accessnow.org/publication/between-a-hack-and-a-hard-place-how-pegasus-spyware-crushes-civic-space-in-jordan

article cybersecurity indeed iphone iphones jordan learn pegasus pegasus spyware spyware understand