Prosecutors say Crumbley could have stopped the murders if he had taken his son home from school the day of the shooting after he was shown a violent picture the teen drew featuring a gun like the one his father had just bought him.
The prosecution claims the elder Crumbley never locked the gun.
His wife was convicted a month ago on identical charges.
But Crumbley’s defense paints him as a more sympathetic figure and counters that he hid the gun from his son.
Another side of Crumbley came to light during the trial when a judge restricted who he communicates with because he made threats on a jailhouse phone and in an electronic message.
The sanction was delivered while the jury was not present to prevent those incidents from influencing the verdict in the case.
