Several suspects have been arrested during the past week.
The Crown Prosecution Service said it was continuing to advise police in relation to the other suspects arrested during their investigation into Rigby's death.
Earlier it emerged that British security services gave a clean bill of health to Adebolajo after he was detained allegedly trying to join Islamic militants in Somalia.
The full extent of British involvement in securing the release of Adebolajo was disclosed for the first time, raising further questions about how much MI5 knew about the alleged murderer.
It also emerged that Adebolajo benefited from the help of British diplomats to avoid a formal deportation after his arrest in Kenya in 2010.
Contrary to previous reports, a Kenyan immigration source told the Daily Telegraph Adebolajo was returned to Britain on an ordinary flight, and not deported, after High Commission officials intervened.
A Kenyan lawyer who represented the 28-year-old said his client was freed from arrest in the town of Lamu, Kenya, three years ago on the recommendation of the British High Commission.
Wycliffe Makasembo said: "Our own intelligence in Kenya were reluctant to release him, but it is the British High Commission which recommended that the suspect be released. It is the British themselves who defended him from our law enforcers."
He said the British diplomatic mission replied in a letter to the police that "gave a clean bill of health that Michael Adebolajo had no criminal record or any connection with any criminal or terrorist organisation in the world".
Kenyan anti-terrorism police detained Adebolajo and six others when they tried to travel north to Somalia in a speedboat. They were suspected of attempting to go to train with the al-Qaeda-linked Islamist militant group al-Shabaab in Somalia, and appeared in court in Mombasa.
Adebolajo was returned to Britain and the other six, all Kenyans, were also released without charge.
A spokesman for the Foreign and Commonwealth Office declined to comment on the lawyer's allegations.
A Kenyan immigration source confirmed to the Daily Telegraph that Adebolajo departed as a passenger on a Kenya Airways flight in November 2010 following British High Commission intervention, and was not deported. According to the same source, there is no evidence of other visits to the country by Adebolajo using his official travel documents.
