A 23-year-old man has been arrested following a court hearing in which Ben Blakeley admitted he had killed his girlfriend Jayden Parkinson, 17.
Thames Valley Police said threats were allegedly made against someone in the public gallery during the hearing at Oxford Crown Court on Monday.
The man from Didcot was arrested today after a public order offence was reported in Craven Way later that evening.
Police say the incident is being linked to the court hearing.
The suspect is currently in police custody.
Blakeley, 22, of Christchurch Road in Reading, has admitted killing Jayden in December and disposing of her body but denied murder and will face trial in June.
A 17-year-old Didcot boy, who cannot be named, denied perverting the course of justice.