If you were trying to develop tactics for using bioweapons, you would want to release something less deadly, but deadly enough to expose the defenses of your opponents.
The less-deadly exposure would also serve to reduce the panic that might occur in future bioweapons attacks, rendering them more effective due to lowered defenses.
Lol.
Ah. So the first shot from the bio weapon guys would be designed to stealthy infiltrate defenses and weaken the city gates. Then the kill shots come.