Suicide bomber Salman Abedi killed 22 people May 22 at Manchester Arena, police said.
He's been arrested on suspicion of offences contrary to the terrorism act.
A police spokesman said: 'As it stands 18 people have been arrested in connection with the investigation, of which six people have been released without charge'.
Earlier on Friday, police evacuated a part of Rusholme after discovering a vehicle that "may be significant to the investigation".
On Friday police located a white Nissan Micra in a auto park of a block of apartments in the Rusholme area of Manchester that they believe could point to Abedi's whereabouts between May 18 and 22 in the lead-up to the bombing at the pop concert.
Officers evacuated an area of the city while they evaluated a white Nissan Micra and have asked people to avoid the area, the BBC reported.
Authorities reportedly believe 22-year-old Abedi, from Manchester, made two phone calls to numbers in Libya - where his family lives - that were not registered to his relatives.
Ten men remain in custody for questioning in connection with incident on 22 May.
The singer photographed with nurses at the hospital and dozens of other patients including 14-year-old Evie Mills, who was visited by the Queen in the same hospital days after the attack.
According to testimony from current and retired intelligence officials, Abedi met members of the Katibat al-Battar al-Libi, an Isis unit based in Syria, who had travelled to Tripoli.