The skulls of two 16-year-olds have been removed from a family grave in an escalating 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 said 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.
Their skulls have not yet been found, police confirmed.
Detective Superintendent Adrian Green said: "We believe that the damage to the graves is part of an ongoing feud between members of travelling families."
In the past fortnight, two homes in the Darlington area have been attacked with vehicles. In the first a stolen horse box was smashed into a bungalow and six days later a recovery truck was driven into a house.
Mr Green said the attack at the small graveyard, little bigger than half a football pitch, was part of the wider feud.
Police have previously said the two incidents with the vehicles could have been linked to an earlier petrol bomb attack.
He added: "You will be aware there have been a number of incidents across the region, specifically in Darlington as well, and we believe they are linked."
The senior detective said the brothers were both 16 when they died.
"You will appreciate this has been very distressing for the family and continues to be so, given the circumstances.
"I think anyone would agree, from whatever community you might come from, that this is a depraved act and the community doesn't have to stand for this."
He said any information about the grave attack or the wider feud would be treated "with the utmost confidentiality".
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.
A large white protective tent remained at the cemetery.
One local, who asked not to be named, said: "This is shocking. Who could do that?"
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."
Gareth Price was found hanging at Lancaster Farms Young Offenders Institution in 2005, the day before he was due to be sentenced for rape.
An inquest found he had been let down by a series of people in authority.
In a statement released afterwards, his family said: "What hurts the most is that we now know that experts had seen Gareth while he was in prison and predicted that he was at a high risk of killing himself at the time of the sentence.
"We were never told this and neither were the prison officers who were looking after him at that time."
According to reports, Levi Price was found hanging in a shed in 2001. The coroner found he could not be sure the teenager intended to kill himself.
Relatives of people buried in the small graveyard have been visiting the scene since the cordon was put up.