Six adults were shot in Colorado Springs, in the US state of Colorado, just after midnight on Sunday (local time) after the gunman stormed a party where three members of the same family were celebrating their birthday.
He shot dead six adults – including his girlfriend Sandra Ibarra-Perez, 28, Melvin Perez, 30, and his wife Mayra Ibrarra De Perez, 33, Jose Ibarra, 26, Jose Gutierrez, 21, and Joana Cruz, 52.
Colorado Springs Police Lieutenant Joe Frabbiele revealed details about the incident in the wake of the tragedy, and said the suspect opened fire on the six adults before taking his own life because he was upset he had not been invited to the gathering.
He added the families of Mr Perez and his wife Mayra were celebrating the birthday party with three children, aged 2, 5 and 11 also in attendance.
Lt Frabbiele said the suspect arrived at the residence alone and shot all six victims in quick succession.
It is believed the children had been in the room at the time but ran to a nearby bedroom to hide.
Children witnessed shooting
One adult managed to escape unharmed and called 911 while the children were also uninjured.
"The children were in close proximity to the shooting event, and to some degree, witnessed what happened," Lt Frabbiele said in a press conference.
"Three additional family members, two aged 16 and one 18, had left the residence shortly before the shooting to retrieve an item from a neighbour and were unaware the shooting had occurred.
"They returned to the residence to discover what happened prior to the police arrival. They attempted to render aid and gave shelter to the younger children."
Jose Guiterrez was still alive when police arrived on scene however later succumbed to his injuries.
Suspect displayed power and control issues
The gunman was named as 28-year-old Teodoro Macias and police said he had been in a relationship with victim Sandra Ibarra-Perez for about a year.
Colorado Springs Police Chief Vince Niski said in a press conference the "horrendous act" was one of domestic violence.
"The suspect who was in a relationship with one of the victims displayed power and control issues in this relationship," he said.
"When he wasn't invited to a family gathering, the suspect responded by opening fire and killing six victims before taking his own life."
Lt Frabbiele added the suspect had a history of controlling and jealous behaviour towards his girlfriend.
"This behaviour in particular was most obvious for trying to isolate her from her family, and making efforts to prevent her from attending family events," he said.
"There are no previously reported occurrences of domestic violence between the two ... the suspect does not have a criminal history."
Man left party with wife hours before shooting
Freddy Marquez told the Denver Post he had been at the birthday party with his family just hours before the deadly shooting unfolded.
He left with his wife and children about 10pm as his wife had to work on Sunday morning.
Mr Marquez described the party as "calm and relaxed" and they watched a boxing match and shared cupcakes.
"It was all family, so everything was fine," he told the Denver Post.
"It's just crazy, it's not what we expected on Mother's Day.
"I'm at a loss for words."
He added he did not know the suspect well but his wife's mother and two brothers were killed in the mass shooting.
"They were loving people," he told the publication.
"Caring, happy. They'd give you the shirt off their back."
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