In the months before the attack on Westminster, Khalid Masood had been living in Birmingham. Here's what we know about him so far.
Man Arrested At Birmingham Airport On Terror Charges
A 21-year-old man has been arrested at Birmingham Airport on suspicion of terrorism.
Waheed Ahmed, the son of a Labour councillor, was detained in Turkey earlier this month along with eight of his relatives as they allegedly tried to cross the border into war-torn Syria.
Greater Manchester Police said they are working to ensure the safe return of the rest of the group, which included four children aged one, three, eight and 11.
In a statement, the force said: "In the early hours of Tuesday 14 April 2015, a 21-year-old man was arrested on suspicion of CPI Section 40 (1) (b) Tact 2000 (Commission, Preparation or Instigation of acts of Terrorism) at Birmingham Airport.''
Late yesterday a 31-year-old man was arrested in Rochdale for the same offence.
The group, which included two women aged 47 and 22, three men aged 24, 22 and 21, and the four children, were stopped in Turkey's Hatay province, close to the Syrian border, on April 1.
Labour councillor Shakil Ahmed said he thought his son had been in Birmingham on a work placement when he discovered that he had been detained in Turkey.
Police searched Mr Ahmed's home earlier this month for clues to why his son had travelled to the country.
After the group were detained, Greater Manchester Police said they had uncovered "no evidence whatsoever'' of any imminent threat to the Rochdale community or elsewhere in the UK.
In a statement following his son's initial arrest in Turkey, Mr Ahmed, a councillor who represents the Kingsway ward on Rochdale Borough Council, said: "I was shocked, worried and extremely upset to hear that my son has been arrested on the Turkey/Syria border.
"It's a total mystery to me why he's there, as I was under the impression he was on a work placement in Birmingham.
"My son is a good Muslim and his loyalties belong to Britain, so I don't understand what he's doing there. If I thought for a second that he was in danger of being radicalised, I would have reported him to the authorities.
"He's studying a degree in politics and sociology at Manchester University and has a good future ahead of him. I just want to speak to my son and get him home as soon as possible so I can find out what's going on.''
Two men from Birmingham remain in custody after a search for accomplices to the Westminster terror attack has seen 11 arrested this week.
A total of seven people have now been arrested after raids in Birmingham over the terror attack in Westminster.
Jess Phillips MP has written to pupils at Holy Family Catholic Primary school, who were in Westminster yesterday.
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