A court has kept a 14-year-old boy in custody over the killing of his 45-year-old mother in Plovdiv. Prosecutors in Plovdiv say the boy planned the killing and was not acting in a fit of rage.

The court heard the case behind closed doors this morning because the accused is a minor.

The mother was found dead on 9 October in an apartment in Plovdiv. The boy himself called the 112 emergency number, said what had happened and helped investigators from the moment police arrived. The suspected weapon has been found and seized.

Prosecutors have not made the motive public. Deputy regional prosecutor Anna Vikova said: "We have no information about earlier conflicts. The motive is extremely personal and linked to the family." Investigators say the relationship between mother and son was difficult.

About three months ago, the boy was accepted at a new school, and he and his mother moved to Plovdiv. His parents have been separated for years. Senior commissioner Vasil Kostadinov, head of the Plovdiv regional police directorate (ODMVR), said the boy lived in Stara Zagora with his grandmother and grandfather until the move.

"He is a first-year student at one of the good schools in Plovdiv," Kostadinov added. The Plovdiv police directorate says it has no information that the boy had been in trouble with the law or was known for problem behaviour.

Expert examinations and other steps in the investigation are continuing. Prosecutors must establish the exact order of events and what the relationship between mother and son was like before her death.