Civilians also count as enemies for this achievement.
Heist: Jewelry Store, Normal - Offline
Items: 2 ECM Jammers with maximum time (30s) + pager delay.
Load the mission, mask up
ECM jammer on wall
run into store, kill 4 civilians with shurikens
take loot and leave, using your second ECM if necessary.
Achievement will unlock on completion of heist.