A mass murderer in Dallas who killed eight at a shopping mall, including three children, subscribed to white supremacist ideology and vilified minorities and women, authorities told US media outlets on Monday.
Police had previously said they were unsure of the motive for the killings.
The gunman, identified as Mauricio Garcia, also wounded ten people at the Allen Premium Outlets mall in Allen, Texas, before being shot dead by police.
He was armed with an AR-15 assault rifle that is capable of firing hundreds of rounds per minute and has been the subject of calls for a ban on rapid-firing weapons in the US.
Several states, including New York, California and Maryland have banned the weapon.
Investigators combing social media accounts linked to the gunman found hate-filled posts aimed at racial and ethnic minorities, NBC News reported, citing two law enforcement officials.
At the time of the shooting, Garcia also wore a patch bearing an RWDS insignia, a symbol associated with violent right-wing extremists, including the Proud Boys, according to news media organisations. RWDS stands for “Right Wing Death Squad”.
The term has often been used to describe far-right anti-communist groups in Latin America who were accused of killing thousands of civilians in the 1970s and 80s.
The New York Times, citing its own law enforcement sources, reported Garcia was believed to have posted a number of messages on a Russian social media platform praising Hitler, sympathising with neo-Nazi beliefs and disparaging women.
The massacre is among the latest in at least 202 mass shootings recorded in the US this year, according to the non-profit group Gun Violence Archive.
The group defines a mass shooting as any in which four or more people are wounded or killed, not including the assailant.
On Sunday, US President Joe Biden renewed calls for Congress to ban assault weapons and high-capacity ammunition magazines.
He asked legislators to enact measures requiring universal background checks and put an end to the immunity currently enjoyed gun manufacturers.
In a surprise move, a committee of the state House of Representatives on Monday approved legislation to raise the minimum legal age for purchasing certain semi-automatic rifles from 18 to 21 in Texas.
The measure was sponsored by Democratic politician Tracy King, whose district includes the city of Uvalde, where 19 children and two teachers were killed in a mass shooting about a year ago.
