JOHANNESBURG — Oscar Pistorius’ murder trial began a new phase Monday when the Olympic athlete arrived at a state psychiatric hospital for a monthlong evaluation whose terms have been described by some as favorable to the double-amputee runner.

Pistorius, who killed girlfriend Reeva Steenkamp in his home last year, sat in the passenger seat of a black sedan and spoke on a cellphone as he arrived behind a police van at Weskoppies Psychiatric Hospital in Pretoria, the South African capital.

The judge who will deliver a verdict in the case asked the hospital to determine if Pistorius had a mental disorder at the time of the shooting, which could affect whether he should be held criminally responsible.

Pistorius must arrive by 9 a.m. and can leave by 4 p.m. each weekday, and has weekends off under an order from Judge Thokozile Masipa. Pistorius, who is free on bail, has been staying at the upscale Pretoria home of his uncle.

Pistorius’ outpatient status troubles some experts who say 24-hour observation is common in state psychiatric facilities becausenursing staff can get additional insights into a patient’s mental state in off hours

“There is a benefit” to the after-hours observation, said Lee-Ann Hartman, a clinical psychologist who has worked in state psychiatric facilities.