An ex-soldier killed his girlfriend's six-year-old son then shot himself dead on a Facebook Live stream.
Jovonie McClendon Jr, 33, shot and wounded his girlfriend Di’eisha Patterson, 27, before going on to murder her son Carter.
He then took his own life in scenes broadcast on Facebook Live.
United States Postal Service worker McClendon opened fire just after calling police and his mum to tell them: "I'm sorry."
US authorities say Di’eisha remains in a critical condition after the attack in Miami Township, Ohio.
The killer's mum phoned 911 and told the operator: "He just called me a minute ago and said that he loved us and that he killed his girlfriend and her baby."
Distressing footage, since removed by Facebook, shows a calm McClendon holding a pistol to his head before pulling the trigger.
He told Facebook friends on the stream "it's been a long day" and "it's been nice knowing you all".
A friend told US media outlet WHIOTV that McClendon was suffering from PTSD following his military service.
Pal Jordan King said: "I believe he lost control. He raged out and he did what he did… There was no coming back from that.”
A police statement said: "McClendon called dispatchers telling them he shot his girlfriend and her son.
"He proceeded to shoot himself while live on Facebook. At this time, we have not determined a motive for the shooting.
"The police department has no history of interactions involving McClendon.
"Township investigators are working with our federal law enforcement partners as well as the United States Postal Service as this investigation continues.