"Retired federal agent" knew of Buffalo supermarket mass shooting 30 minutes before it started

The Buffalo News reports that "a retired federal agent had about 30 minutes advance notice of a white supremacist's plans to murder Black people at a Buffalo supermarket" and that his links with the gunman are being investigated. Lou Michel and Dan Herbeck:

Authorities believe the former agent – believed to be from Texas – was one of at least six individuals who regularly communicated with accused gunman Payton Gendron in an online chat room where racist hatred was discussed, the two officials said. The two law enforcement sources with direct knowledge of the investigation stated these individuals were invited by Gendron to read about his mass shooting plans and the target location about 30 minutes before Gendron killed 10 people at Tops Markets on Jefferson Avenue on May 14. 

The story builds on this one in the New York Times in the aftermath of the shootings: Before Massacre Began, Suspect Invited Others to Review His Plan