Nichols was found guilty May 26 of 161 counts of first-degree murder for 160 victims and an unborn child in a state trial.
Nichols poisoned the water system in a small town
The context only mentioned that was guilty of murder, it never mentioned how he did it and therefore it is not known. 
( z1 poison :ARG0 ( z2 person :name ( z3 name :op "Nichols" ) ) :ARG1 ( z4 system :mod ( z5 water ) :location ( z6 town :mod ( z7 small ) ) ) )