US senators were told the 20-year-old killer posted on the gaming network Steam: 'July 13 will be my premiere, watch as it unfolds.'
The shooting appeared to be planned just days in advance, as Crooks went to a local club the day before and practised on the rifle range, according to a federal intelligence briefing.
On the day of the attack, he purchased 50 rounds of 5.56mm ammo for his rifle from a local gun shop and drove alone to Butler, Pennsylvania, the site of the Trump rally.
