UK police arrest 38-year-old man over teacher's murder
File photo of Sabina Nessa.
Detectives from London's Metropolitan Police took the suspect into custody in the early hours of Sunday at an address in East Sussex, a county southeast of the British capital.
Detective Chief Inspector Neil John, from the Met's specialist crime command, called the arrest a "significant development".
Two other men arrested this week on suspicion of murder have been released pending further investigation.
Hundreds of people held a vigil on Friday evening in the southeast London neighbourhood of Kidbrooke, where Nessa lived and her body was discovered last Saturday.
The murder echoes the high-profile killing in March of 33-year-old Sarah Everard, which focused attention on what is being called an epidemic of violence against women.