Investigators are examining a message left on a gaming platform site purported to have been authored by the suspect, according to multiple law enforcement sources briefed on the probe.

Investigators, according to multiple law enforcement sources, found a post on the gaming platform Steam that is credited to the suspected gunman, 20-year-old Thomas Matthew Crooks. The post reads, "July 13 will be my premiere, watch as it unfolds." Investigators are working to determine whether the post is legitimate.

Investigators are still working to determine a motive behind the attempted assassination of former President Donald Trump.

Crooks had been registered as a Republican voter, according to state records. But a $15 donation to a progressive group was also recorded under "Thomas Crooks" in January 2021, according to FEC records.

This post has been updated based on additional information from the FBI.

Thomas Matthew Crooks, the suspected gunman in the assassination attempt on Donald Trump last Saturday, searched on his phone for the dates of the former president’s rally in Butler, Pennsylvania, and for dates of the Democratic National Convention in Chicago, sources familiar with the investigation told ABC News.

Crooks also searched on his phone for images of both the former president and current president, sources said.

The suspect’s phone search history revealed no indication of his political views.

-ABC News' Aaron Katersky

Law enforcement officials investigating the assassination attempt on Donald Trump told lawmakers today in an unclassified briefing that 20 minutes passed between the time Secret Service snipers first spotted Crooks on the roof and the time shots were fired at the former president, according to several law enforcement officials and lawmakers briefed on the matter.

According to this source, briefers said the snipers spotted him on the roof at 5:52 p.m. ET. The shooting happened at 6:12 p.m., 20 minutes later.

The briefing was conducted by the FBI Director, his Deputy Director and the head of the USSS.

In addition, briefers told lawmakers Crooks was identified as a person of interest a full 62 minutes before the shooting took place.

From the time he fired his first shot to Crooks being killed was just 26 seconds, according to law enforcement officials. Eleven seconds after the first shot, USSS counter snipers acquired their target -- and 15 seconds after that, Crooks was shot dead.

Former President Donald Trump is not expected to attend the funeral of Corey Comperatore, the 50-year-old spectator who was shot and killed at Saturday's rally, sources told ABC News.

Comperatore, a firefighter, died shielding his family from the gunfire, officials said. He’s survived by his wife and two daughters.

Comperatore’s obituary said friends can pay their respects on Thursday. Funeral services will be private, the obituary said.

-ABC News’ Soorin Kim, Kelsey Walsh and Lalee Ibssa