Dallas - Missouri police said on Sunday evening an off-duty officer had fatally shot a man trying to get into his house and a relative said the two had been arguing on Facebook about the Black Lives Matter movement.
St Louis County police say 20-year-old Tyler Gebhard threw a concrete planter through a window to enter the officer's Lakeshire home on Saturday evening. The officer, who wasn't identified, then shot him.
Police say Gebhard was known to the family and had recently made online threats toward them.
An uncle of Gebhard's, Patrick Brogan, told The St Louis Post-Dispatch that Gebhard and the officer had been arguing on Facebook. He said Gebhard, who was biracial, empathised with the objectives of the Black Lives Matter group.
Police Chief Jon Belmar said the officer was on leave.
Meanwhile, the White House has announced that President Barack Obama will travel to Dallas on Tuesday and deliver remarks at an interfaith memorial service.
Five officers were killed and seven were wounded when a gunman opened fire on a protest march in Dallas on Thursday.
The attack occurred shortly after Obama had arrived for a Nato summit in Poland. He cut his visit to Spain short by a day and has spoken daily during the trip about the attacks, calling for police and protesters to "listen to each other".