A man and a woman have been arrested on suspicion of an acid attack that left a 21-year-old woman from Dagenham disfigured and partially blind.
A 21-year-old woman and a 28-year-old man have been arrested on suspicion of causing grievous bodily harm.
The suspects have been bailed.
Police said they were trying to establish the full circumstances of the attack. They had have previously appealed for a male dog walker and two women to come forward.
A police statement said: "These three people have now been traced.
"Police would like to speak with a potential witness who got on the Route 368 Bus at Barking railway station and got off at Lodge Avenue at around 0045hrs on 30 December.
"He is described as a black man, around 20 to 30 years, 5'5" in height and of medium build, wearing a black jacket and a black hooded top with blue jeans.
"Officers are appealing for this man to come forward, and are asking anyone else who may have seen the victim in Lodge Avenue or seen anything suspicious around the time of the attack."
Oni decided to publish pictures of herself after the attack because the police had so few leads about the perpetrator. She has also appeared on ITV's This Morning to speak about the ordeal.
She was left with serious burns to her head, neck, arms and body and said her life has been "destroyed" by the attacker.
"I look in the mirror and it just isn't me. I'll never look the same again," she said.
Speaking to the Evening Standard, Oni also spoke about claims that she had thrown acid in her own face: "I've only just come out of hospital after having surgery on my eye. To see this story saying that I'd done it made me so angry and really hurts.
"There's no way I would have done this to myself. I want the person who did this to be caught."
Oni said she was attacked by someone wearing a Muslim niqab. However, police have not been able to find any sign of the alleged attacker on CCTV footage.
Investigators were reported in some media to have seized Oni's laptop over claims that she had searched the internet for information about acid attacks. A police spokesperson would neither confirm nor deny these allegations.