(CNN)Police said they have uncovered "significant evidence" in the Manchester Arena bombing investigation and they want the public's help.
Manchester Police uncover 'significant evidence' in bombing
Greater Manchester Police found a gym bag (described as a holdall) in a white Nissan Micra seized in the Rusholme area of Manchester, on June 2. Investigators said bomber Salman Abedi made repeated trips to and from this car between May 18 and 22.
"We believe he was taking items from the car to help assemble the device," police said.
"Forensic examination has uncovered significant evidence inside. We now need any information you might have about this holdall. Did you see someone in the Rusholme area with this holdall or recognize the one on the photo?"
Abedi detonated a bomb that killed 22 people -- many of them children and young people -- who were leaving an Ariana Grande concert at Manchester Arena.
Police said the car was sold by its previous owner on April 13 and that Abedi left the country on April 15.
"It is vital we understand what happened to this car during these few days," police said. "We need to know who was in the car and where it went."
Police said they are making "significant progress" in the investigation of the May 22 attack. A 38-year-old man was arrested at London's Heathrow Airport in connection with the attack, police said in a statement late Tuesday. The statement said the man was arrested on suspicion of "offenses contrary to the Terrorism Act" and remains in custody.
Police said the arrest was planned and there was no direct threat to the airport. A total of seven men remain in custody for questioning.
Though Abedi seems to have acted alone the night of the attack, police said that doesn't mean he did not have help in the lead-up.
"It is vital we exhaust all our lines of inquiry to establish how this was planned and understand how others might have been involved," police said.