Dr Suraj Shenoy said he did not accept evidence from other psychiatrists that Moses Christensen was suffering from a psychotic breakdown when he killed 70-year-old Richard Hall.
Christensen, 22, of Corser Street, Stourbridge, West Midlands, denies murdering Mr Hall on the grounds of diminished responsibility.
Giving evidence to jurors at Stafford Crown Court on Tuesday, Dr Shenoy was asked to comment on the circumstances of Mr Hall's death on August 13 last year on Shropshire's Brown Clee Hill. Mr Hall lived in Perton, South Staffordshire.
The consultant psychiatrist said prosecution case papers, medical records and a video link meeting with Christensen in January had led him to the view that the defendant had "some autism traits".
The case so far:
The expert witness told jurors that clips from body-worn camera footage from officers who detained Christensen on August 13 did not show clear evidence of psychotic behaviour.
Dr Shenoy said: "From his actions, from his speech, from his account, I could not find any concrete evidence to say he had lost touch with reality.
"From his account I could not see any evidence to say he did anything he did not want to do."
Christensen had been thinking about killing someone for a number of weeks, Dr Shenoy said, adding: "He knew exactly what he was doing at the time.
"He formed his intent. He formed a clear plan and he acted out that plan.
"He set out with a goal and he achieved that goal."
Claiming mental illness had not directly influenced Christensen's behaviour on the day of the killing, and that he understood the nature of his conduct, Dr Shenoy continued: "He is acting rationally and he is not acting impulsively, which would support my view.
"He did take care not to alarm Mr Hall - he hid the knife so as to have an element of surprise. He was not acting randomly or in a frenzy."
While in custody after the alleged murder, Dr Shenoy said, Christensen was suffering from a psychotic breakdown caused by "the shock of the killing itself and his subsequent incarceration" and his "loss of role".
Under cross-examination, Dr Shenoy rejected an assertion that it was clear that Christensen was suffering from psychosis in the days leading up to the killing.
Although he conceded Christensen was psychotic in November and December 2019, Dr Shenoy said he could see no evidence to support claims he was suffering a similar episode on August 13.
The consultant told the jury: "If the evidence was clear we would have seen clear evidence on the body-worn footage from the police."
Jurors at Stafford Crown Court have been told they must decide whether Christensen is guilty of murder or manslaughter by reason of diminished responsibility.
The trial continues.