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LONDON — The attacker who bombed an Ariana Grande concert in Manchester wasn't part of a large network, but other people involved in the crime may still be at large, a senior police officer said Thursday.

Police may make more arrests in the investigation into the attack, said Russ Jackson, head of counterterrorism policing for northwest England.

Salman Abedi, a Briton of Libyan heritage, detonated a home-made knapsack bomb as crowds were leaving Manchester Arena on May 22, killing 22 people and himself. More than 200 others were wounded.

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In the days after the attack, police arrested 22 people on suspicion of terrorism offenses and said they had rounded up a large part of Abedi's network. But all the suspects were subsequently released without charge.

"We don't have evidence of a large network," Jackson told reporters at an update on the investigation. "We do, however, suspect others were either aware or complicit in the knowledge of this attack."

Jackson said the investigation "is likely to run on for many more months to come."

This undated photo obtained on May 25, 2017 from Facebook shows Manchester-born Salman Abedi, suspect of the recent Manchester terrorist attack. File AFP - Getty Images

"We are examining all sorts of lines of inquiry and it is possible more arrests and searches will take place," he said.

Detectives want to question Abedi's younger brother Hashem, who has been detained in Libya, and are "engaging with" British prosecutors and Libyan authorities, Jackson said.

A Libyan counterterrorism official has said Hashem Abedi knew that his brother was planning something, and said Salman Abedi had been radicalized in Britain.

"We are still working to understand the manner by which he became radicalized," Jackson said.