Virginia - The killing of a man in Stilte Park, Meloding, in Virginia, was a barbaric act, Free State police MEC Butana Komphela's office said on Thursday.
Such “inhuman acts” undermined democracy, his spokesman Saki Mohono quoted him as saying.
On Tuesday evening, Tshidiso Klaas was stoned and stabbed to death when a crowd attacked him at his home.
Warrant Officer Malebo Khosana said on Thursday nine people had been arrested for various offences relating to the incident, but no one was yet charged with Klaas's murder.
Two were taken into custody on Tuesday for public violence, another was subsequently caught with a dangerous weapon in his possession and six others were arrested on Wednesday for public violence.
Two others facing public violence charges were due to appear in court on Thursday.
Khosana distanced himself from the claim that the crime was a vigilante killing, but said investigations were continuing.
Komphela called for strong action to be taken against those involved in Klaas's murder.