Kent-born terrorist Khalid Masood, who killed five people and injured more than 50 in an attack on Westminster here, was known as a potential extremist in 2010, it emerged as the police made a fresh arrest in connection with the investigation on Sunday night. Masood first came to the attention of MI5 six years ago after returning to the U.K. from Saudi Arabia where he had been teaching English, the Guardian confirms. British Prime Minister Theresa May has also confirmed that Masood had previously been investigated by the intelligence services but merely as a \u201cperipheral\u201d figure. Meanwhile, counter terror squads arrested a 30-year-old man after the latest in a string of raids in Birmingham. The man, who was detained on suspicion of preparation of terrorist acts, brings the total number of arrests to 12. Also watch: Speaking on Sunday, a spokesman for the Metropolitan police said, \u201cA new arrest has been made as part of the investigation being carried out by the Met\u2019s counter terrorism command into the Westminster attack.\u201d The Met also confirmed that a 58-year-old man was detained under terrorism legislation. Nine others were released without charge, while a woman from Manchester was released on police bail.