Copeland maintained he had worked alone and had not discussed his plans with anyone. During police interviews, he admitted holding neo-Nazi views, and talked of his desire to spread fear and trigger a race war. He told police, "My main intent was to spread fear, resentment and hatred throughout this country; it was to cause a racial war." He said, "If you've read The Turner Diaries, you know the year 2000 there'll be the uprising and all that, racial violence on the streets. My aim was political. It was to cause a racial war in this country. There'd be a backlash from the ethnic minorities, then all the white people will go out and vote BNP."
After his arrest, Copeland wrote to BBC correspondent Graeme McLagan, denying that he had schizophrenia, and telling McLagan that the "Zog" or Zionist Occupation Government was pumping him full of drugs in order to sweep him under the carpet. He wrote, "I bomb the blacks, Pakis, degenerates. I would have bombed the Jews as well if I'd got a chance." Ryan writes that Copeland's first idea had been to bomb the Notting Hill Carnival, after seeing images of the 1996 Atlanta Olympics bombing. When asked by police why he had targeted ethnic minorities, he replied, "Because I don't like them, I want them out of this country, I believe in the master race." Whilst on remand, Copeland also wrote to crime writer Bernard O'Mahoney, who posed as a woman called Patsy Scanlon in the hope of duping Copeland into confessing. According to The Independent, the letters helped secure a conviction by giving prosecutors evidence about Copeland's state of mind.
Copeland's mental state was assessed at Broadmoor Hospital. He was diagnosed by five psychiatrists as having paranoid schizophrenia, while one diagnosed a personality disorder not serious enough to avoid a charge of murder. There was no dispute that he was mentally ill, but the extent of this, and whether he was unable to take responsibility for his actions, became a matter of contention. At the Old Bailey, Copeland's plea of guilty to manslaughter on the grounds of diminished responsibility was not accepted by the prosecution or jury.
He was convicted of three counts of murder and planting bombs on 30 June 2000, and given six concurrent life sentences. The trial judge spoke of his doubt that it would ever be safe to release Copeland.
On 2 March 2007, the High Court decided that he should remain in prison for at least 50 years, ruling out his release until 2049 at the earliest, when he would be 73. Copeland appealed; on 28 June 2011, the Court of Appeal upheld the ruling.