If the researcher is not being arrested its not "kill the messenger". Impounding his equipment, the "evidence", is just a very rude way of getting his data on vulnerabilities and attacks. They could have asked. Then again perhaps they feared the "evidence" being tampered with, confidential sources and all that sort of thing. Again, rude, but a plausible path if such concerns were warranted.
In the U.S., they can take all of your stuff if they arrest. Well, technically they can't, because that would be unconstitutional and illegal, but they DO. So how much worse is it when they can take all of your stuff without even arresting you?