I'm going to give this one an attempt.

The problem is that it is impossible to know what he actually thought - everything he said or wrote was with the understanding that other people would read it, and he did put a lot of effort into saving face. Whether he truly regretted his actions, however, is not something we will ever know.

Speer's efforts to look good started before he was even captured - he cooperated willingly with a US team sent to Flensburg to investigate the effect of bombing on German cities (Tusa 35). At that time, he was in the 'Flensburg government', which officially ruled for the few days between Hitler's death and the surrender but hung around for a while because nobody was sure what to do with them. On May 23, the British finally put an end to the charade and the 'government' was arrested. Speer continued to try to impress his captors. He admitted the crimes of the Nazis, did not try to defend Hitler, and continued to willingly tell his interrogators everything about how the armaments industry had worked.

On the stand, Speer gave a vague and half-assed admission of general responsibility, also denying his knowledge of atrocities such as the Holocaust.

SPEER: [...] I should like to say something of fundamental importance here. This war has brought an inconceivable catastrophe upon the German people, and indeed started a world catastrophe. Therefore it is my unquestionable duty to assume my share of responsibility for this disaster before the German people. This is all the more my obligation, all the more my responsibility, since the head of the Government has avoided responsibility before the German people and before the world. I, as an important member of the leadership of the Reich, therefore, share in the total responsibility, beginning with 1942. I will state my arguments in this connection in my final remarks.

DR. FLACHSNER: Do you assume responsibility for the affairs covered by the extensive sphere of your assignments?

SPEER: Of course, as far as it is possible according to the principles generally applied and as far as actions were taken according to my directives.

DR. FLACHSNER: Do you wish to refer to Fuehrer decrees in this connection?

SPEER: No. Insofar as Hitler gave me orders and I carried them out, I assume the responsibility for them. I did not, of course, carry out all the orders which he gave me. (IMT vol. 16 p. 483)

Not much of an admission, that. In his final statement, there was not a word about regret or remorse, but there was a jab at the Soviets - he ended the statement with "May God protect Germany and the culture of the West." (IMT vol. 22 p. 407) He did, however, make an impression on many people. His claims at being an apolitical professional who got in over his head were believed by many. As Norman Goda writes, "If Speer had been bewitched by Hitler while millions of Jews and others mysteriously vanished, then was this not an alibi for all Germans struggling to master the past?" (Goda 178)

Speer took his twenty-year sentence calmly, telling the psychologist that it was only fair. Once in prison, he continued to pretend to be fine with everything, but in secret, he carried out a lengthy correspondence with an old friend that was exclusively dedicated to getting him freed as soon as possible. His friend, an unreformed Nazi, was not impressed with the hypocrisy.

None of those attempts are in his published books. How sincere is the remorse contained there can only be guessed at, but we do know for certain that he wanted to hide his secret attempts at early release from the world. Those attempts failed, and it was only in 1966 that he was able to tell his idea of what had happened to everyone.

In his interviews and books he stuck to the same line - he continued to insist that he hadn't known about the Holocaust, a claim that is obviously preposterous now but was believed by many back then. When Matthias Schmidt, a PhD student, wrote a scathing biography of him in 1981 as his dissertation, Speer tried to block the publication, but he died before any decisions could be made and the dissertation went ahead with no issues.

Now that we do know that he lied about so much while also admitting responsibility for terrible things, it invites the question of how sincere these admissions were. Of course, many others simply put up a wall of denial or refused to talk to the press, but admissions did reap benefits - the moniker 'the good Nazi', for example. How much of what he did admit was the desire to look good and how much was the desire to be honest can only be guessed at, but we do know for certain that he concealed a lot of things and outright lied about more, making him a very unreliable narrator indeed.

Works cited:

Tales from Spandau by Norman Goda

The Nuremberg Trial by Ann and John Tusa

Trial of the Major War Criminals Before the International Military Tribunal: Proceedings Volumes