Some clothing was found by deputies that they believe he left behind.
McCartney was a husband and has three sons.
"He chased after him and there were shots fired", sheriff's spokesman Ed Troyer said in an interview.
In a statement earlier from the Governor's office, Jay Inslee asked all Washingtonians to hold Deputy McCartney's Family in our hearts as well as all the men and women in Pierce County Sheriff's Department who served with McCartney and all who serve in law enforcement across our state. He leaves behind a wife and three young boys, who are four, six, and nine years old.
Police say two suspects were involved. An active manhunt is under way for his suspected shooter. A large containment area around the shooting scene was blocked off for several hours while authorities searched for a second suspect. He was last seen wearing a dark hooded sweatshirt and a black beanie.
"Our thoughts and prayers are with Pierce County Sheriff's Office as they seek justice and peace for their Deputy killed in the line of duty", Thurston County Sheriff's Office posted on Twitter.
There are road closures as a result, and the Bethel School District has now chose to close its schools today.