Now Shaker Aamer is back in the UK, these are the questions we have to ask

When the former UK resident Shaker Aamer was taken to Guantánamo, Tony Blair was less than halfway through his stint as prime minister, the Queen hadn’t yet celebrated her golden jubilee and social media channels like YouTube and Facebook were unheard of.

On 14 February 2002, Mr Aamer - aka prisoner #239 - was secretly flown into the recently-opened US military detention centre in Cuba. Like those before him and those that would follow (779 in all), Aamer was brought in shackles, ear muffs and a blindfold from halfway across the world. He’d already been held for months in harsh conditions in Afghanistan. He hadn’t seen a lawyer. He hadn't been able to communicate with his family or anyone in the outside world.

While he couldn’t possibly know it, this was just the start of Mr Aamer’s ordeal. The rest is fairly well-known: long years at Guantánamo, many in solitary confinement; battles to get a lawyer; allegations of routine violence from camp guards; bitter hunger strikes in protest at conditions and interminable detention; “approvals” for transfer out of Guantánamo that we're never honoured.

Aamer, one of the first taken to Guantánamo, has seen hundreds of fellow detainees (finally) released, but his own long-expected liberation has been endlessly stalled. Why, we still don't know.

Now that he’s finally arrived back in Britain, 13 years and eight months after he was first bundled off a US military transport plane in Cuba, we need answers to some very pressing questions. Who ordered his detention and interrogation in Afghanistan in the first place? Is it the case, as Mr Aamer has always alleged, that MI5 officers were in the room as US interrogators beat him up in Afghanistan, including by bashing his head against a wall so hard it was “bouncing”? Were MI5 feeding questions during the Americans’ abusive interrogations of Aamer in Afghanistan (as they appear to have done in other “war on terror” cases), and if so who was telling them to do this?

Other questions abound in this most concerning of cases. We were repeatedly told that the UK government were holding “discussions” with the USA over Mr Aamer’s release. These discussions have taken years, so what on earth were they about? Last year the Home Secretary Theresa May confirmed that her officials had liaised with US counterparts ahead of the publication of the US Senate Intelligence Committee’s report on CIA torture. This, she claimed, was in the interests of “security”. In whose interests were the protracted Aamer discussions?

It took until August 2007 for the UK government to accept that it should even seek the release of former UK residents held at Guantánamo. Others besides Shaker Aamer - Jamil el-Banna, Bisher al-Rawi and Binyam Mohamed - were for years completely abandoned. Given reports that secret UK intelligence have played a highly disreputable part in these men's rendition, alleged abuse and detention, this is one of the many scandals involving the UK and Guantánamo.

How can the UK begin to redeem itself in relation to all this? That it descended deep into a US mire of CIA rendition and torture, of unlawful interrogations and the travesty of justice at Guantánamo is well-known - but did it do so willingly, and if so on whose say so? For answers to this and much else we still need the independent judge-led inquiry that David Cameron long ago promised.

Shaker Aamer’s harrowing Guantánamo ordeal is over, but we still don't know why it ever happened. We can’t turn the clock back to February 2002, but we can still ensure that there is some semblance of justice for Mr Aamer and others.