William Brock told investigators he shot Loletha Hall because he thought she was working with a man who called and threatened him and his family. Hall didn't threaten Brock and didn't have a weapon or assault him, according to the sheriff’s office and court documents.
Dude on the phone was attempting extortion. When someone dies in the commission of a crime, everyone gets hit with the murder charge.
See:
https://www.themarshallproject.org/2015/09/24/a-person-can-be-charged-with-murder-even-if-they-haven-t-killed-anyone
Felony murder laws vary by state. In Ohio, felony murder does not apply to extortion.