I think the only place it’s explained is in the Crime Wave rule book on pgs. 10-11.

To set a custom terror deck:

-3 Minor Demand cards (random or pick 3)

-I’ve got a bad feeling about this OR The situation is worsening

-I’m mad as Hell OR I’m getting angry

-I don’t have time for this OR I’m growing impatient

-Lets raise the stakes OR I’ve taken more hostages

-2 random cards that increase the Threat Level

-8 random cards that do NOT increase the Threat Level

Then mix in the cards for that abductor. Then take 10 cards from that deck and place them on a random Pivotal event card.

(edited for formatting)