Greater Manchester Police on Monday released two photos and asked for the public's help in their investigation of the May 22 attack that killed 22 after an Ariana Grande concert.
"Did you see Abedi with this suitcase between the 18 and 22 May 2017?" Detective Chief Superintendent Russ Jackson asked in a statement. "Where did you see him with it during that time?"
"We have no reason to believe the case and its contents contain anything dangerous, but would ask people to be cautious," said Jackson.
Police said the attacker had the suitcase in at least two Manchester neighborhoods.
"We believe Abedi was in possession of this case in the days before the attack," Jackson said. "I want to stress that this is a different item than the one he used in the attack."
The May 18-22 timeline is crucial, because it's known that Abedi returned from Libya just a few days before the bombing.
As of Monday evening, British investigators had not determined whether Abedi built the bomb he used, a British counterterrorism official told CNN terrorism analyst Paul Cruickshank. The official said that is the key question being asked by investigators.
Authorities over the weekend published CCTV images of Abedi on the night of the attack, which show him wearing a hat, glasses and a dark top.
The suitcase development came as Home Secretary Amber Rudd confirmed intelligence service MI5 is launching an internal review on how much it knew about Abedi
before the attack.
Rudd's comments follow media reports over the weekend that the agency was alerted to Abedi's extremist views before he blew himself up. ISIS has claimed responsibility for the atrocity.
The Mail on Sunday newspaper
reported that the FBI told MI5 in January that British-born Abedi, who was of Libyan descent, was part of a North African Islamic State cell plotting an attack in the United Kingdom.
Rudd declined to comment on exactly what was known about the 22-year-old bomber, during an interview with Sky News.
Asked during the interview: "Are you happy that MI5 should be investigating themselves?" Rudd replied, "I think it is right that they do this. In the future, we can look at anything else that might need to be done. As a first step, it is absolutely right."
She added: "There's a lot of information coming out about what happened, how this occurred, what people might or might not have known.
"I think it's right that MI5 takes a look to find out what the facts are. We shouldn't rush to make any conclusions at this stage."
The BBC reported
that MI5 was alerted three times over Abedi's extreme views. The Guardian newspaper
reported the agency launched two inquiries into how it missed the danger he posed.
In a BBC television interview
on Sunday, Rudd was quizzed over whether MI5 has the resources to keep on top of the terror threat.
She said MI5 is looking at 500 plots and has identified 23,000 jihadist extremists, of which 3,000 are on a "top list." She said MI5 is currently recruiting 1,900 new staff and its budget "has gone up significantly."
"We will make sure that we put the right resources in to keep people safe always," she added.
When CNN asked the Home Office for a response to reports the FBI warned MI5 about Abedi, a spokesman declined to comment.
A British counterterrorism official told CNN it was not clear whether Abedi received training with ISIS in Syria.
On Thursday, a US official told CNN the bomber likely received some ISIS training by traveling to Syria in the months before the attack. The British official, who spoke to CNN on Monday, said that based on the latest information, UK investigators at this stage saw this as a possibility, rather than a probability.
The investigation brought the arrest
of a 23-year-old man in Sussex, south of London, on suspicion of terrorism offenses. Sixteen arrests have been made in the investigation so far.