Police in London have arrested a second man in connection with Friday’s terror attack on a Tube train. The 21-year-old man, arrested Saturday, joins an 18-year-old suspected of helping to carry out the terror attack. British Home Secretary Amber Rudd said there is enough evidence to suggest that the attack wasn’t a lone-wolf incident. Rudd added that officials do not believe ISIS was responsible for the attack. Immediately after the attack, the U.K. raised its terror level to critical.