"Caroline was not able to share this blessing with Matthew," Rittner's friend Sarah Marie posted to Facebook. "It’s an amazing blessing and Matthew’s legacy will not only be lived through their son but now their daughter who is expected to arrive into this world in October!"
Rittner's friend shared news of the pregnancy on the date marking three months since the officer was killed while helping serve a warrant for suspected illegal guns and drugs at a Milwaukee duplex.
"[The news] was met with mixed emotions," police Lt. Kristin Felsman told WISN-TV on Tuesday. "Extremely joyful emotions because, [it's] another legacy of Matt, and obviously very sad emotions because Matt would not be there to share in the joy of a new life."
Rittner held a gender reveal party with her husband's unit, where they released pink balloons from a box to signal she's having a girl. Rittner and his wife also have a son.
Sgt. Roberto Colon told CBS58 the department will be there for the family going forward.
"She knows that she can come anytime and knock on our door. She doesn't even have to. We're gonna be there bothering her all the time anyway," he told the television station. "She'll probably have to kick us out of the house most of the time."
Suspect Jordan Fricke has pleaded not guilty to three charges, including first-degree intentional homicide. He’s scheduled for trial beginning July 8.
A Go Fund Me page has been set up on behalf of Matthew Rittner's family, for those who would like to donate.
The Associated Press contributed to this report.