Investigators said they were unsure of the attacker’s motives. But clues pointed to an isolated and increasingly troubled life, and no accomplices.

The alleged gunmen in the shooting, Sajid Akram, 50 and his son, Naveed Akram, 24, were from Bonnyrigg, a diverse, multilingual suburb miles from Sydney’s Bondi Beach.

He was a foremost authority on the president, tracing his career in unvarnished accounts from his time as California governor through his years in the White House.