I need to witness the death of a sim.

If you do not want to starve/drown sims, you could move in an elder as a rommate soon as your sim decides on his Public Enemy Aspiration. Then, while the sim is doing the first tiers of the aspiration, the elder is gradually growing older and will die naturally eventually. If "witness a sim die" is the only requirement left that you have to meet for Public Enemy, switch to another aspiration, move in the elder and switch back to PEnemy once the Elder is close to dying.

(b.t.w., I think the requirement is a bit over the roof. It´s something evil sims will enjoy, but not every Public Enemy aspiration sim is neccessarily evil. Just like irl not every misanthrope would go out and kill people).