CARDIFF, Wales — He was born in Singapore, but his family moved back to Britain when he was a child. He had family problems and was known by locals as belligerent and aggressive, with a drinking problem. He had Muslim neighbors, who described his behavior as fairly unremarkable, and his children had Muslim friends.

No one on the cul-de-sac in Cardiff, Wales, where Darren Osborne, 47, lived could readily explain what he is believed to have done: rented a van, driven it 150 miles to London and plowed into a crowd of Muslims as they finished prayers at the Finsbury Park Mosque early Monday.

Numerous residents here said that Mr. Osborne was often agitated, even disturbed, but few described him as frightening and none said he had expressed political sentiments, much less anti-Muslim or far-right ones — until last weekend, when he was kicked out of a local pub, the Hollybush, after a drunken tirade.

“My son was at the pub on Saturday night and said he got kicked out because he was scribbling all over the tables and shouting racist comments about Pakistanis and Muslims,” a resident, Ross Johnson, said Tuesday outside the pub.

Image Darren Osborne Credit... Swns

The authorities have not formally identified Mr. Osborne as a suspect. But British news organizations, including the BBC, have named him, and friends and family members recognized him as the man arrested after Monday’s attack. The man was arrested on suspicion of the commission, preparation or instigation of terrorism including murder and attempted murder.

The police raided Mr. Osborne’s house on Monday, and officers have been posted outside.

The assault wounded several people; seven remain hospitalized with a range of injuries. A man who had been receiving first aid at the scene died hours later, but it was not clear whether the attack had directly caused his death. Mr. Osborne was pinned down by bystanders after the attack and was shielded by an imam and other men before being hauled away by the police.

Prime Minister Theresa May of Britain called the act a terrorist attack targeting Muslims, and it was widely seen as yet another assault on the cosmopolitan, multicultural British capital, which had already experienced two terrorist attacks since March. It also raised questions about where the line between terrorism and hate crimes can be drawn, and whether the distinction is even meaningful, particularly in cases of severely disturbed individuals.

Several residents in and around Glyn Rhosyn, the street where Mr. Osborne lived in a semidetached two-story house, said he at times seemed disturbed and volatile.

Chris Peter, a car mechanic, said that he used to work with Mr. Osborne but that he had found Mr. Osborne to be “unreliable” and “erratic.”