Police will begin questioning one of the men suspected of murdering Drummer Lee Rigby in Woolwich, a week after the soldier's death.
Michael Adebowale, 22, was shot by police after apparently charging towards armed officers in the aftermath of Drummer Rigby's death, but was moved into police custody yesterday after he was discharged from hospital.
A second murder suspect, Michael Adebolajo, 28, who was also shot by police, remains in hospital under police guard.
Relatives of Adebolajo released a statement sending their "heartfelt condolence" to Drummer Rigby's family, and saying there is no place for violence in the name of religion.
The Adebolajo family said: "Nothing we can say can undo the events of last week. However, as a family, we wish to share with others our horror at the senseless killing of Lee Rigby, and express our profound shame and distress that this has brought to our family.
"We send our heartfelt condolence to Lee Rigby's family and loved ones."
Drummer Rigby was hacked to death near Woolwich barracks in south east London last Wednesday and Adebowale and Adebolajo were both arrested on suspicion of his murder.
Adebowale was further arrested on suspicion of the attempted murder of a police officer.
Meanwhile prison chiefs have linked an attack on a prison guard to the soldier's murder and warned staff of an increased risk of threats, according to reports.
A male warder was left with a broken cheekbone after being held hostage by three male prisoners, two aged 25 and one aged 26, at HMP Full Sutton in Yorkshire on Sunday.
An email circulated to staff in top-security jails and young offender institutions and seen by The Times said: "Three Muslim prisoners took an officer hostage in an office.
"Their demands indicated they supported radical Islamist extremism.
"All staff are reminded to remain vigilant to the increased risk of potential attacks on prison officers inspired by these and last Wednesday's events."
Counter-terrorism officers have been brought in to investigate the attack at the maximum security jail, during which a female warder was also injured.
So far, 10 people have been held by detectives investigating the young soldier's death, including Adebowale and Adebolajo.
These include a 50-year-old man, arrested on Monday, who was released on bail yesterday.
A 22-year-old man arrested in Highbury, north London, on Sunday and three men detained on Saturday over the killing have all been released on bail, as has a fifth man, aged 29.
Two women, aged 29 and 31, were arrested on suspicion of conspiracy to murder but later released without charge.
The family of Adebolajo said they "wholeheartedly condemn" terrorism, and "fully expect" that Drummer Rigby's killers will be brought to justice.
The statement said: "We wish to state openly that we believe that there is no place for violence in the name of religion or politics. We believe that all right thinking members of society share this view wherever they were born and whatever their religion and political beliefs.
"We wholeheartedly condemn all those who engage in acts of terror and fully reject any suggestion by them that religion or politics can justify this kind of violence.
"We unreservedly put our faith in the rule of law and with others fully expect that all the perpetrators will be brought to justice under the law of the land."
In the wake of the attack it emerged that Adebolajo and Adebowale were both known to MI5.
Adebolajo was also arrested by Kenyan authorities three years ago because they feared he was attempting to join an al Qaida-linked militant group, the country's anti-terrorism police said.
The murder has sparked a flurry of activity by the English Defence League, including a march of 1,000 supporters to Downing Street on Monday chanting "Muslim killers off our streets" and "There's only one Lee Rigby".
A massive police presence kept them separate from a smaller group of anti-fascist activists, with officers making 13 arrests in total for a range of public-order offences.
Forces charity Help for Heroes announced it will not accept any donations raised by EDL leader Tommy Robinson or other members of the group, or any political party.
Police are now investigating two attacks by vandals on the RAF Bomber Command memorial and the Animals in War memorial in London.
Both were daubed with graffiti and although the words written on the two memorials have now been covered up, it is thought "Islam" had been written on each of them.
Home Secretary Theresa May has strongly indicated she would seek to revive legislation giving security agencies access to public communications data.
Her disclosure came after Downing Street confirmed the launch of a new terror taskforce to crack down on extremism.
The group, comprising Cabinet ministers and top police and security service officials, will focus on radical preachers who seek out potential recruits in prisons, schools, colleges and mosques.