Metropolitan Police said the friend, identified by the BBC as 31-year-old Abu Nusaybah, was wanted himself on suspicion of "the commission, preparation or instigation of acts of terrorism." The force declined to elaborate.
In his BBC interview, Nusaybah said he knew Adebolajo as a moderate Islam convert. He said he thought Adebolajo's behavior changed after a trip to Kenya last year, and alleged that Britain's MI5 domestic spy agency tried to recruit him upon his return six months ago.
Rigby's killing — and Adebolajo's apparent link to Islamic extremism — has stirred anti-Muslim backlashes across Britain. Police said they arrested three people on suspicion of posting racist tweets ahead of the English Defense League march, and further detained 24 others before and during the protest on suspicion of public drunkenness, vandalism and distributing racist literature. One group of marchers carried a sign that read "Taliban Hunting Club."
About 350 counterdemonstrators who called themselves Newcastle Unites shouted abuse at the marchers, including "Nazi scum off our streets!" The region's Northumbria Police said riot police prevented any direct clashes between the opposed groups.
Meanwhile, the far-right British National Party announced it would rally supporters next weekend on the spot where the young soldier was killed.
"Has the horror of Woolwich woken you up too? ... Join the British resistance," British National Party leader Nick Griffin said in a video address Saturday to supporters announcing his plans for a "Stand Up to Muslim Terror" rally at the scene of the crime, where thousands already have left floral bouquets paying tribute to the soldier.
A group that campaigns against extremism, Faith Matters, said it has received reports of around 150 anti-Muslim hate crimes across Britain since the soldier was killed Wednesday, more than 10 times the usual rate. Its director, Fiyaz Mughal, said he was particularly concerned by how geographically widespread the actions, including street fights and the vandalism of mosques, had become.