Salman Abedi, the bomber in the Manchester terror attack, wasn't part of a large network, but other people involved may still be at large, a senior police officer said on Wednesday.

Police may make more arrests in the investigation into the attack, Russ Jackson, head of counterterrorism policing for northwest England, said July 6.

The Islamic State claimed responsibility for the May 22 concert bombing that killed 22 people, plus Abedi, and wounded more than 200 others. Here's what we know.

The bomber, Salman Abedi

British officials said Abedi had been on the radar of the country's intelligence services but was considered a peripheral figure.

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

Jackson said police have reconstructed Abedi's movements in the weeks before the attack, as he obtained components and built his deadly device.

On the day of the bombing, Abedi spent several hours carrying the bomb though central Manchester before he detonated it in the foyer of Manchester Arena as an Ariana Grande concert was wrapping up.

Abedi's parents came to Britain early in the 1990s, and he reportedly was in contact with family members just before the attack.

Abedi was born in Britain to a Libyan family, grew up in Manchester's southern suburbs and once attended Salford University there. He was a business management student but dropped out, according to The Telegraph.

Neighbors recalled Abedi as a tall, thin young man who often wore traditional Islamic dress and did not talk much.

"He was such a quiet boy, always very respectful towards me," a member of the Libyan community in Manchester recalled to The Guardian. "His brother Ismail is outgoing, but Salman was very quiet. He is such an unlikely person to have done this."

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That perspective clashed with others. Mohammed Saeed, with the Didsbury Mosque and Islamic Centre told the newspaper he had once delivered an anti-terrorism sermon. Abedi did not like what he heard, Saeed said.

"Salman showed me a face of hate after that sermon," he recalled. "He was showing me hatred."

Abedi was driven to extremism after seeing a friend fatally stabbed last year, a female relative said. He complained of being treated badly in Britain and was troubled why there seemed to be no outrage over his friend's death, she said.

Abedi believed it was because the friend was Muslim, according to the relative.

She said that Abedi also referred to Britons as "infidels" who "are unjust to the Arabs." She defended him as "a great kid" and said he had no links to ISIS or other militant groups.

However, Abedi is believed to have traveled to Syria and had "proven" links with ISIS, French Interior Minister Gerard Collomb has said.

Abedi's father, Ramadan Abedi, denied in May that his son was linked to militants or to the deadly attack. He said that when he spoke to his son in recent days, he sounded "normal.”

"We don't believe in killing innocents. This is not us," the elder Abedi told the AP by telephone. "We aren't the ones who blow up ourselves among innocents. We go to mosques. We recite Quran, but not that."

He said his son had visited Libya and never visited Syria.

Abedi spent three weeks in Libya prior to the Manchester bombing, returning to England just days before the attack, two U.S. defense officials confirmed to Fox News.

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What do we know about his father, Ramadan Abedi?

Ramadan Abedi fled Tripoli in 1993 after Moammar Gadhafi's security authorities issued an arrest warrant for him. He eventually sought political asylum in Britain. Now, he is a manager for the Central Security force in Tripoli, Libya's capital.

He has denied having ties to any of Libya's militant groups, including the Libya Islamic Fighting Group, which was linked to Al Qaeda.

However, former Libyan security official Abdel-Basit Haroun told the AP that the elder Abedi was a member of the group in the 1990s. Although it disbanded, Haroun said the father now belongs to the Salafi Jihadi movement, the most extreme sect of Salafism from which Al Qaeda and ISIS both hail.

Ramadan Abedi was arrested in Libya after the attack and is still being held, The Guardian reported.

What about Abedi's brothers?

Ramadan Abedi confirmed that another son, 23-year-old Ismail, was arrested in Manchester.

And Salman's younger brother, 18-year-old Hashem, was taken into custody in Libya. Hashem was in contact with Salman, Ahmed bin Salem, the spokesman for a counter-terrorism force told Reuters.

"We have evidence that he is involved in Daesh (ISIS) with his brother," bin Salem said. "We have been following him for more than one month and a half. He was in contact with his brother and he knew about the attack."

Hashem was allegedly plotting an attack in Tripoli, Reuters reported.

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Back in Britain

All 22 people arrested on suspicion of terrorism offenses have now been released without charge, Greater Manchester police said last month. Salman's brother Ismail was released, the Financial Times reported.

Jackson said last month that some of those arrested had offered "accounts which explain innocent contact with Abedi." He said at the time that risk to the public had been considered before the suspects were released.

Suspects arrested under terrorism laws can be held for up to 14 days before they must be charged or released.

"We don't have evidence of a large network," Jackson told reporters July 6. "We do, however, suspect others were either aware or complicit in the knowledge of this attack."

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.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.