their lives on the line to serve and protect. here's abc's clayton sandell with another look at the ambush at copper canyon. >> reporter: it's early morning on new year's eve 2017. five officers from the douglas county sheriff's department. >> sheriff's office! >> reporter: responding to a 911 call. >> sheriff's office! >> reporter: from the copper canyon apartments in highlands ranch, colorado. waiting for them, 37-year-old army veteran matthew riehl. he has a history of mental health issues. >> matt, come out! matt, come out of the room now! >> reporter: and unknown to them, a loaded ar-15 rifle. >> open the door! sheriff's office! [ gunfire ] >> shots fired, shots fired!