"We hoped he could rest in peace," said Stella Byrd, the mother of 1998 dragging victim James Byrd Jr. "They've done enough to him already."
Two people at the Jasper City Cemetery tending to a relative's gravesite Thursday afternoon noticed the damage, police said.
The granite headstone, noting Byrd's date of birth as May 2, 1949, was broken from its base, according to Beaumont television station KFDM.
An obscenity and racial epithet were carved into a small metal plate on the bottom of the broken tombstone. Byrd's name and date of birth are engraved on the plate.
Police Chief Stanley Christopher told the station the desecration apparently happened in the past couple of days. The case is being investigated as criminal mischief, he said. There have been no arrests. The site has been fingerprinted.
City Manager David Douglas said police patrols around the city cemetery have been increased.
The grave has been disturbed before. Not long after Byrd's burial, a small brass nameplate was removed from the site.
Byrd was on his way home from a party June 7, 1998, when he crossed the path of three white men who had been out drinking.
The men took Byrd to a country road, beat him, chained him to their truck by his ankles, and dragged him more than two miles until he was dismembered and decapitated.
Two were convicted and sentenced to death; one received life in prison.
Jasper is about 110 miles northeast of Houston.