It appears, based on initial assessment, that the gunman in, was increasingly frustrated over the political direction of the United States, a law enforcement official told CBS News' Pat Milton.
Officials identified the gunman as James T. Hodgkinson, 66, of Belleville, Illinois.
By mid-Wednesday afternoon, there was no indication that the shooting at a congressional baseball practice was inspired by a terrorist group or terrorist ideology, the source said.
Investigators are looking at Hodgkinson's pathway to violence and the things that may have motivated him to commit a violent act. The law enforcement source told Milton that traditionally, investigators contend that people like the suspect do not just snap, but that anger and emotions simmer over time like a slow-boiling pot.
Investigators are focusing on what could have motivated him by talking to family members, friends and coworkers, and looking into whether there are identifiers on social media. They are also looking at his use of the internet.
The source stressed that this information is based on preliminary assessments in a fluid situation and that the assessments could change, Milton reports.
Hodgkinson, who owned a home inspection business in Belleville, Illinois, opened fire at a baseball field in Alexandria shortly after 7 a.m. Wednesday, law enforcement officials say. He shot Rep. Steve Scalise and wounded four others, including two Capitol Police officers, before being shot himself and taken into custody.
In a statement from the White House, President Donald Trump said Hodgkinson died of his injuries.
Officials say Hodgkinson was carrying an assault weapon similar to an. Both are being traced by the Bureau of Alcohol, Tobacco and Firearms. The FBI has taken over the investigation.
The FBI released a poster seeking information from the public about Hodgkinson.
On his Facebook page, Hodgkinson wrote a number of posts criticizing President Trump and expressing support forof Vermont, who condemned the shooting "in the strongest possible terms" on Wednesday. Hodgkinson had been a volunteer on Sanders' presidential campaign.
The SITE Intelligence Group reports that Hodgkinson "regularly espoused vitriolic anti-Republican and anti-Trump viewpoints while supporting liberal causes on Facebook." His posts didn't overtly warn about Wednesday's shooting, according to SITE, which reported that he often used "hyperbole and foul language in expressing his opinions."
CBS News' Kristin Steve and Laura Strickler report that, according to local court records and incident reports from the St. Clair County Sheriff's Department in Illinois, Hodgkinson had over 20 interactions with law enforcement for minor offenses.
Court records show he had seven convictions in total for misdemeanors since 1978. One conviction in 2009 was for failing to have an electrician's license and another in 1991 was for speeding. The other five charges are too old for the court to have descriptions of the charges, Steve and Strickler report.
In 2006, Hodgkinson was arrested on a misdemeanor charge of battery, court records show. Lyndon P. Evanko, Hodgkinson's former attorney, did not remember the circumstances of the charge but told CBS News that Hodgkinson never did anything violent. The charge was dismissed by a judge.
Evanko said there was nothing that stood out to him to indicate Hodgkinson would do something like Wednesday's shooting, but that he did seem like a bit of a "misanthrope" and "not terribly personable," and had an attitude of "this is how I do things and I should be able to do them my way." Evanko described him as a "very angry little man, very angry person, felt slighted by people."
While Hodgkinson was never charged with a felony, he was accused of violence against a 16-year-old girl who was in his care in 2006, and there appears to be a series of disputes with her, according to court records and incident reports.
Records from the St. Clair County Sheriff's Department show he had multiple run-ins with neighbors, complaining of them turning around in his driveway and damaging his yard.
As recently as March this year, a neighbor complained of him firing his gun in his backyard. According to a police report, a neighbor told police that they heard "50 shots." In the incident, Hodgkinson was found to have a valid license for the gun and was told to not shoot the gun in the area since homes were nearby.
A law enforcement official told CBS News' Milton that Hodgkinson was not on the radar of the U.S. Secret Service. He was unknown to them.