A look at what’s known and what isn’t about the attack in London that left seven people and three attackers dead:

WHAT HAPPENED?

Police say three men drove a van into pedestrians on busy London Bridge just after 10 p.m. Saturday. The attackers, wielding blades and knives, ran down a set of stairs into Borough Market, a well-known fruit and vegetable market that’s also home to popular restaurants and pubs. There they stabbed people in several different restaurants. Seven people were killed and at least 48 were hospitalized. Still others had minor injuries. The whole thing lasted about eight minutes, according to police.

WHO DID IT?

Police haven’t said. The attackers were shot dead by police near the Wheatsheaf pub eight minutes after the incident started. The men were wearing what appeared to be vests with explosives, but Prime Minister Theresa May says they weren’t real and were just meant to cause panic. Twelve people have been arrested in Barking in east London and raids are going on elsewhere. May has characterized the attack as the work of Islamic extremists but no group has claimed responsibility yet.

WHAT ARE THE POLITICAL IMPLICATIONS?

That’s not clear either. There’s an election Thursday that May called in an attempt to increase her Conservative Party’s majority in Parliament. The Conservatives were far ahead in polls but their lead has narrowed in recent days. The main political parties halted national campaigning Sunday but were expected to resume Monday, and officials said the election would not be canceled or postponed.

HAS THIS HAPPENED BEFORE?

This is the third attack in Britain in as many months. Two weeks ago, a suicide bomber blew himself up at an Ariana Grande concert in Manchester, in northwest England, killing 22 people and injuring dozens more. In March, a British convert to Islam ran down people with a vehicle on Westminster Bridge, killing four before fatally stabbing a policeman on Parliament’s grounds. May said Sunday that police had recently foiled five other plots.

(AP)