Assistant Commissioner Mark Rowley of the Metropolitan Police makes a statement outside of New Scotland Yard on March 24 in London. (Jack Taylor/Getty Images)

On the final night of a troubled, disjointed life that began in the affluent English countryside and ended in a deadly rampage on the streets of London, Khalid Masood returned to his roots.

He had lived for years in the British Midlands, known to neighbors as a devoted gardener but otherwise all but invisible, an urban ghost who left few traces after a series of criminal convictions and a mysterious trip to Saudi Arabia.

Yet on Tuesday night, at age of 52, Masood rented a car and drove to southeast England, where he was raised. At a hotel in the seaside town of Brighton — not far from the gentle and well-to-do towns where classmates from his prep school days remembered him as a happy, soccer-loving teenager — he exchanged jokes with the manager and went to sleep.

He was “friendly and smiley” and said he was visiting friends, the manager, Sabeur Toumi, told British broadcasters on Friday.

The next morning, Masood checked out and drove to London to commit the worst act of terrorism on British soil in more than a decade. By the time he was shot dead by security forces inside the gates of Parliament, more than 50 people lay wounded in the shadow of Big Ben, four of them mortally.

A handout photo made available by the Metropolitan Police shows Khalid Masood, the man behind the terror attack in London. (Metropolitan Police Handout/EPA)

[London mayor reassures a city that says it doesn’t need re]

Whether Masood truly acted alone — or whether he had accomplices who aided or encouraged him — was the focus of the police investigation on Friday. So, too, was the question of what had motivated a middle-aged man with no known ties to extremist groups to turn his rental car and a knife into instruments of terror.

“Our determination is to find out if either he acted totally alone, inspired by perhaps terrorist propaganda, or if others had encouraged, supported or directed him,” said Mark Rowley, the acting deputy police commissioner.

Adding to the theory that he may have had help were two arrests Friday that police called “significant.” That brought the number of people in custody in connection with Wednesday’s attack to nine.

Few details about the latest arrests were made public. But they reflected the widening effort to piece together a portrait of the suspect — from his upbringing around England, to his years of small-time crime and his emergence as Khalid Masood, the name he adopted along with other aliases.

[A bang, then screams: Khalid Masood’s attack on the center of British government]

As of late Friday, 17 people remained hospitalized — including two who were in critical condition.

(Jason Aldag,Victoria Walker/The Washington Post)

Most of the injured — and three of the dead — were struck by Masood’s Hyundai SUV as it sped along the sidewalk on the tourist-crowded Westminster Bridge on Wednesday afternoon. After the vehicle crashed into an iron gate that rings Parliament, Masood used a knife to attack and kill an unarmed London police officer, Keith Palmer.

The other three dead were civilians. London police identified the latest fatality as 75-year-old Leslie Rhodes from south London, who died of injuries late Thursday.

Britain’s Sky News and other outlets reported Friday that Masood was on his phone’s Whatsapp messaging program minutes before carrying out his rampage.

Police have said their theory is that Masood, a Muslim convert born in Britain under the name Adrian Russell Ajao, was carrying out “Islamist-related terrorism” that was “inspired” by jihadist groups overseas.

The Islamic State claimed on Thursday that Masood was a ­“soldier” of its self-proclaimed ­caliphate. But the group often makes similar proclamations without providing evidence of ­direct links to attackers.

There were more questions than answers Friday as to when or how Masood had become radicalized. Rowley said that “influences in our community,” “influences from overseas” and “online propaganda” were all being examined.

As part of their inquiry, police said they have seized 2,700 items, including “massive” amounts of computer data.

Analysts cast doubt on the idea that Masood had acted without support, even if he ultimately carried out the attack by himself.

“We need to get away from this lone-wolf thing,” Chris Phillips, former head of the national counterterrorism security office, told the BBC. “There’s almost always someone else involved.”

The attack was just the latest in a major European city, following a string of such mass-casualty events in recent years in Paris, Brussels, Nice, Berlin and beyond.

In Belgium on Friday, a man who had driven a car carrying weapons at high speed in a pedestrian shopping street in Antwerp on Thursday was charged with terrorism offenses. Federal prosecutors charged a man they identified only as Mohamed R., 39, with “attempted murder in a terror context.”

Belgium has been on elevated security alerts since suicide bombers attacked the Brussels airport and a subway station a year ago, killing 32 people. Memorial events to mark the anniversary were taking place across Belgium when Wednesday’s attack in London unfolded

[‘I immediately recognized him’: What we know about the London attacker]

Details were still emerging ­Friday about Masood, who was born on Christmas Day in 1964 in Kent, southeast of London.

But the overall picture was of a life divided into at least three phases: a childhood set in the posh countryside in which he was considered popular and outgoing by friends, followed by a two-decade stretch of run-ins with the law and finally a period of more than a decade in which he seemed to all but disappear – until Wednesday.

“I’m in deep shock,” said Stuart Knight, a classmate for five years at Huntleys, an all-boys school in the leafy and prosperous town of Royal Tunbridge Wells. “I knew him as Adrian Ajao.”

Photos from the era show a teenage Ajao dressed in coat and tie, the only black student in a sea of white faces.

Knight said that the teen’s mother, Janet, was a religious Christian and that the family attended the local church.

“He was a very nice lad, very sporty, very well-liked by all the other students,” said Knight, 52, who runs a butcher shop. “A fun guy to be around. He liked football and he played rugby.”

Knight said the two lost touch after they left the school in 1981, and the attack “certainly doesn’t relate the person I knew all those years ago.”

As an adult, the man who would become Masood racked up a string of criminal convictions, including for assault, and served time in jail. His last conviction came in 2003, for possession of a knife.

It was unclear when he converted to Islam, when he changed his name and what he did professionally.

British news outlets reported Friday that Masood had lived in Saudi Arabia for a time around 2008.

Former neighbors of Masood in Luton, north of London, told broadcasters that he enjoyed gardening, and one thought he stayed at home and looked after his three children. In the Midlands city of Birmingham, where he last lived, community leaders said he was unknown.

He had been investigated by intelligence services. But in a statement, Scotland Yard said Masood was not the subject of any current investigations and had not been convicted of any terrorism offenses.

It is not clear why he drove 180 miles from Birmingham to Brighton, bypassing London, to spend the night at a budget hotel before staging his attack in the capital

The manager of the Preston Park Hotel said his guest was “laughing and joking” after checking into room 228 on Tuesday.

“He talked about his family, his mom, his dad, his wife. He said his dad is ill, and his mom is upset because his dad is ill,” Sabeur Toumi told Sky News.

After Masood paid by credit card and drove away Wednesday morning, Toumi told the BBC, the receptionist noted in the hotel’s systems that he was “a nice guest.”

Murphy reported from Washington.

Read more:

Family of Utah man killed in London ‘heartbroken’

Britons are denouncing Donald Trump Jr.’s attack on London’s mayor

In the aftermath of London attack, some Brits praise their strict gun laws

Today’s coverage from Post correspondents around the world

Like Washington Post World on Facebook and stay updated on foreign news