The original headstones were either missing or had become damaged over the years.
The group Wednesday unveiled a new marker for the grave of Officer George Neil. He was beaten and shot to death in 1930 while defending a black man from a group of four white men.
Investigator Mike Dooley says honoring Neil was something the officers felt they had to do.
So far, they've replaced 50 of the headstones, and they hope to replace 13 more by the end of summer.