Materials could have been traded and the scrolls written near the Dead Sea ... or even folks from the Dead Sea traveled to Jerusalem, used local materials and made some scrolls, and traveled back.
So from that, it's clear to see that extensive trading networks were necessary for these civilizations, not just for luxuries like exotic herbs and spices, but their basic industrial needs.
Seems that lethal dose for arsenic is likely too high to be transmitted by even a pure arsenic trioxide blade, unless it was manufactured with the intent of leaving bits inside the wound, like maybe a blade a rough brittle surface to leave grit. Even so, would have to introduce ~50+mgs worth, which sees like a tall order.
Seems arsenic bronze is even less toxic, so probably not poisoning anyone. I wonder if the minor local toxicity of arsenic blade cuts would reduce the chance of the wound causing sepsis.
As for the movement of writers, or the scrolls post creation, you'd look at where scripts were generated and where they sourced their materials. Just speculating, as I haven't read the background material on this new discovery, but it would make sense that the monasteries in Jerusalem would have a reproducible sourcing process since they would be generating manuscripts often. Same would go for monasteries around the Dead Sea.
But, researchers have to find something to research or they're out of a job.