FBI officers also said James Hodgkinson, who was killed in a shootout with police during last Wednesday's attack at a congressional baseball practice, had "no nexus to terrorism" and acted alone.
"On the shooter, we found a piece of paper that contained the names of six members of Congress," said Andrew Vale, assistant director of the FBI's Washington field office.
"No context was included on this paper. However, a review of the shooter's web searches in the months prior to the shooting revealed... A cursory search of two of the members."
Hodgkinson, who was from Illinois but was living in Virginia at the time of the shooting, launched his attack carrying two weapons, a 7.62mm SKS rifle and a 9mm handgun, according to the Federal Bureau of Investigation.
The guns were purchased legally -- the rifle in 2003 and the handgun in November.
In an accompanying statement, the FBI confirmed that Hodgkinson had made numerous posts on social media platforms "espousing anti-Republican views," but that he did not make any online threats or references to lawmakers or to the congressional baseball practice.
Early on June 14, Hodgkinson sprayed an Alexandria, Virginia baseball field with gunfire, wounding number three House Republican Steve Scalise, a US Capitol Police officer, a congressional aide and a lobbyist before police shot the assailant. Scalise, who was shot in the hip and suffered grave internal injuries, remains hospitalized.
On Wednesday, MedStar Washington Hospital Center upgraded Scalise's condition to "fair," and said the 51-year-old was "beginning an extended period of healing and rehabilitation."