Why not have used "looks for" but "looked for" in the headline?

the story is written in reported speech about an event that had already happened.

The headline says that he sought out (looked for) a certain victim.

But for a headline, don't we usually use present tense to express it?

It's often done that way, yes, Ori - when it makes sense, when the issue has a sense of ongoingness to it. In this case, it's clearly a finished event.

Headlines are written for a particular purpose; to catch the eye, and pique some interest in the reader.
Also, they have to be very brief.

So I would say, for a student of English, there's not much to learn in considering particular headlines. Headline writing is a specialism.

It's something that happened the day before they wrote the headline. He wasn't still looking for the administrator. It was over and done. Past tense is appropriate.

Thank you all