Police say a man was detained and bailed on suspicion of helping Abdul Shokoor Ezedi.
A 22-year-old man has been arrested and bailed on suspicion of assisting the alleged Clapham alkali attacker.
Abdul Shokoor Ezedi has been on the run since a woman and her two young girls were hurt in south London on Wednesday.
The Metropolitan Police said a man was detained on suspicion of helping Ezedi following a raid early on Monday.
They added that there had been a new sighting of Ezedi in the Southwark Bridge area on Wednesday night.
The 31-year-old woman injured on Wednesday remains sedated in hospital and could lose the sight in her right eye, police told reporters, adding that her injuries will impact her for the rest of her life.
Officers are trying to establish how long Ezedi and the woman have known each other and what sort of relationship they had.
Police also confirmed that Ezedi is not the father of the woman’s children who were hurt in the attack. Police have said the children’s injuries are not as serious as first thought.
Five Met Police officers were also injured as they responded to the attack, as were four members of the public who tried to help.
Met Police Commander Jon Savell said a 22-year-old man was arrested for assisting an offender at 00:45 on Monday at an undisclosed location.
The suspect was taken to a police station in south London, where he was interviewed before being released on bail.
“If people are harbouring Ezedi they do potentially commit an offence and we take that very seriously and we will take action,” Cmdr Savell said.
Police have two main hypotheses about Ezedi’s whereabouts: that he has come to some harm, or that someone is looking after him.
The last sighting of Ezedi – a convicted sex offender thought to be from Afghanistan – had previously been Tower Hill underground station, at 21:33, on Wednesday.
Police say they have new CCTV images showing Ezedi in the Southwark Bridge area at 21:50 on the same day.
Police are not currently searching the River Thames for Ezedi.
Investigators are trawling through hundreds of hours of CCTV and tracked Ezedi’s movements on the Tube network via his bank card, which was last used on Wednesday, police said.
The focus of the investigation remains London and Newcastle, but police forces across the country have been put on high alert and UK Border Force and the National Crime Agency are assisting the search.
A £20,000 reward for information leading to his capture has been offered by the Metropolitan Police.
Nick Aldworth – a former senior counter-terrorism police officer – told BBC Radio 4’s Today programme police forces offer rewards for information “when there is a sense someone is hiding within the community”, possibly with help from others.
He said it was also “not unlikely or improbable” the suspect had taken his life and “there is a body to be found”.
Mr Aldworth added it would be difficult for someone to move around London publicly for several days without being picked up on CCTV.
Before this week, 35-year-old Ezedi was living in the Newcastle area. He is believed to have travelled to the UK on a lorry from Afghanistan in 2016.
Police say he has a serious injury, which could make him more recognisable.
On Saturday, armed officers were called to Manchester Piccadilly railway station after a reported sighting of Ezedi. British Transport Police said it was a “false alarm”.
Ezedi travelled to London from Newcastle in the early hours of Wednesday and the attack happened outside a hotel in Lessar Avenue at 19:25 GMT.
Police have previously confirmed they found a “very strong concentrated corrosive substance” after searching his Newcastle flat.
Ezedi was picked up on CCTV at a Tesco shop in Caledonian Road, Islington, north London, at 20:38.
At 21:00, he was seen on camera entering King’s Cross underground station and boarding a southbound Victoria line train.
He arrived at Victoria Station in central London at 21:10 and changed trains to travel eastbound on the District line at 21:16, police said.
Ezedi was seen leaving Tower Hill underground station a few minutes later. The latest sighting shows him walking on Allhallows Lane, in the Southwark Bridge area, at 21:47.
The BBC has confirmed Ezedi was convicted of a sexual offence in 2018.
The Crown Prosecution Service (CPS) said he was sentenced on 9 January 2018 after pleading guilty to one charge of sexual assault and one of exposure.
He was given a suspended sentence at Newcastle Crown Court and put on the Sex Offenders Register for 10 years.
Ezedi was later granted asylum after two failed attempts. He was allowed to stay in the country after a priest confirmed he had converted to Christianity.
The Catholic Church covering the North East of England has previously confirmed Ezedi was a client of a charitable project it ran which “assists a wide range of people who come to us in need”.
In an update on Monday, the same church organisation said: “After checking local parish records and central records and after consulting with clergy we have no indication that Abdul Ezedi was received into the Catholic faith in this diocese or that a Catholic priest of this diocese gave him a reference.
“We do not know which Christian church received him nor which Christian minister gave him a reference.”
Speaking to reporters on Monday, Prime Minister Rishi Sunak would not be drawn on whether immigration laws should be changed after reports claiming religious conversions may be being used to bolster asylum applications.