[shakna]

> Nobody would use the word "in" at that location in the sentence.

Except that was, once upon a time, a very common phrasing. As the writer was coming from the 60/70s, you need to adjust your expectations of English.

"in trying to" is actually incredibly common for what might be called "Oxford English". You'll still find it in heavy use in newspapers.

So rather than suggesting the speaker is making a deliberate mistake, or is not a native speaker, it might simply be suggesting a formal education - something that already matches the profile of the Zodiac killer.

[ehnto]

I still use and hear phrasing like that, given I am Australian in a state where the Queens English held tight that makes sense to me.