The skulls of two 16-year-olds were removed from a grave in a "sickening" escalation of a feud between travelling families, police said.
A graveyard in Metal Bridge, County Durham, has been cordoned off since Saturday afternoon when it was first discovered that a grave had been disturbed.
Durham Constabulary officers believe the incident, which included damage to a headstone, took place on Friday night.
The grave belonged to Levi George Price and Gareth Price, who were both 16 when they died in 2001 and 2005 respectively.
Detective Superintendent Adrian Green said: "We believe that the damage to the graves is part of an ongoing feud between members of travelling families."
He added: "This has taken things too far. It is depraved and goes against the religious and cultural beliefs of decent people."
Police have pleaded with those involved in the row to settle their differences and for any witnesses to come forward.
Regular police patrols will take place in key areas "to deal robustly with any further disturbances", Mr Green said.
He assured residents the crime was targeted and did not involve the wider community.
A large white protective tent remains at the cemetery.
One local, who asked not to be named, said: "They have been there all weekend. The officers in their white suits have been working there.
"We don't know what has been going on, we haven't been told anything.
"But there's more to this than a damaged headstone."
People in the small village, on a busy road that links to the A1 near Durham, have talked about something being taken away in an estate car with blacked out windows.
Another man said: "On Saturday night I had a walk up the street and you could see them working in the darkness, they had floodlights on and they were taking photographs."
Relatives of people buried in the small graveyard - little bigger than half a football pitch - have been visiting the scene since the cordon was put up.