MANCHESTER, England — The suspect in the deadly Manchester concert bombing was driven by what he saw as unjust treatment of Arabs in Britain, a relative said Thursday, confirming he made a final phone call in which he pleaded: “Forgive me.”

Salman Abedi was particularly upset by the killing last year of a Muslim friend whose death he believed went unnoticed by “infidels” in the U.K., said the relative, speaking on condition of anonymity over concerns for her own security.

“Why was there no outrage for the killing of an Arab and a Muslim in such a cruel way?” she asked.

“Rage was the main reason” for the blast that killed 22 at the end of an Ariana Grande concert at Manchester Arena on Monday, she said, speaking by telephone from Libya.

The new insight into Abedi’s motivation came as Britons faced stepped-up security, authorities pushed forward with raids and the investigation extended across Europe into Libya, where most of the suspected bomber’s family lived.

The number of arrests in the U.K. ticked up to eight as British Transport Police said armed officers would begin patrols on some trains because of an increased threat of terrorism. Greater Manchester Police Chief Constable Ian Hopkins said, without elaborating, that searches of suspects’ homes brought “very important” clues in the probe of the bombing. But leaks from the investigation were creating a trans-Atlantic diplomatic mess.

Manchester police halted their sharing of investigative information with the U.S. through most of Thursday until receiving fresh assurance there would be an end to leaks to the media.

British Prime Minister Theresa May, who spoke about the matter with President Trump at a NATO summit in Brussels, said the countries’ partnership on defense and security was built on trust. But “part of that trust is knowing that intelligence can be shared confidently,” she said.