Here's what you need to know about last night's terror attack in London

London was devastated again late Sunday evening by the fourth terror attack in four months when an unidentified man driving a white van plowed into pedestrians leaving a local mosque. Here is what we know so far, and don't know yet, about the attack.

What we know:

• Witnesses said the suspect mowed down pedestrians leaving the Finsbury Park Mosque a little after midnight as the crowd left the mosque after their Ramadan prayers. (Fox News)
• The crowd had assembled to render assistance to an elderly man who had collapsed when the van struck. Ten victims suffered injuries of varying severity; the elderly man was pronounced dead at the scene (of as yet unknown causes).  (The Guardian)
• All of the victims were members of London's Muslim community. (Fox News)
• A 48-year-old suspect, who has been described by witnesses as caucasian, has been taken into custody and police are treating the attack as terrorism. (Fox News)
• Witnesses reported that the man exited the van yelling "I want to kill Muslims," before he was taken to the ground by onlookers. (The Guardian)
• The suspect can be seen on video blowing a kiss and waving to bystanders as he was taken to a local hospital for a mental health evaluation. (The Independent)
• Finsbury Park Mosque has been home in the past to several Islamist terrorists, including imam Mostafa Kamel Mostafa who is currently serving a life sentence for killing four people, and shoe bomber Richard Reid who attempted to detonate explosives packed in his shoe on an American Airlines flight in December 2001. The Mosque has taken steps in recent years to distance itself from Islamic terrorism. (Slate)

What remains unclear:

• Witnesses told reporters that two other men jumped out of the van and fled the scene, but British police claim the suspect in custody acted alone. (Fox News)
• The suspect's identity has not yet been released by British authorities.
• Though police are treating the attack as revenge for the Islamist terror attacks taking place in Manchester and on London Bridge, evidence of a motive has not yet been conclusively established.  (The Guardian)

What it all means:

• The terrorist alert in the UK has been moved to "severe," which indicates an attack is highly likely. (The Guardian)
• British Muslim leaders have requested additional security outside local mosques, according to The Guardian.
• White supremacist groups on social media have praised the attack, while Islamic State supporters have already started using the attack to incite a response. This means an escalation in violence is highly likely. (The Guardian)