One theory for the decision to target Trump rather than Mr Biden was that the rally at Butler was only 51 miles from his home in Bethel Park, a drive of 1 hour and 21 minutes.
He was a light user of social media but did have an account with Discord, a group chatting app.
“We have identified an account that appears to be linked to the suspect; it was rarely utilised and we have found no evidence that it was used to plan this incident, promote violence, or discuss his political views,” a Discord spokesperson said.
The Princess, who is recovering from cancer, has no plans to visit the US, with her public engagements having been scaled back since the diagnosis, which she announced in March.
Last week, King Charles and Queen Camilla were pulled out of a public engagement in Jersey because of a security scare.
They later resumed the visit after it turned out to be a false alarm.