A man accused of fatally stabbing a 71-year-old retiree in her National City home last week had initially posed as a door-to-door salesman before later ambushing her, beating her with a rock then attacking her with her own kitchen knives, a prosecutor alleged Monday. Noel Trevino, who prosecutors believe was a stranger to the woman, allegedly killed Wanda Taylor when she returned alone to the house she shared with her husband on Division Street near D Avenue around noon Wednesday, prosecutors said.