Hi, I'm writing a short story and these two parts are highlighted with green in Word (ungrammatical). Can someone tell me what's wrong? Thanks in advance

"Last week we brought the horrifying news of the 95-year old retired marine, by the name of John Doe, who went off on one of the most macabre and sadistic killing sprees ever to be seen in the state of California. "
"Those who lived to tell the tale report that Mr. Doe appeared to act fully in cold blood - his face being completely expressionless."