The women came to visit their brother at his home and spent the night in his spare bedroom, they told investigators. They woke up to Rivera repeatedly stabbing them with a knife, the arrest report said.
The woman told police she tried to fight him off, but he kept stabbing her. The younger sister ran from the room, the report said. The woman told police she was finally able to push him away and call police.
Neighbours told officers they woke up to a loud banging sound at their front door They found a woman covered in blood and begging for help, the report said.
"He's trying to kill me! Please help my sister," the arrest report said the woman told neighbours. As the door was opened, the neighbours saw Rivera walking by, also covered in blood, the report said.
"Shut the door," Rivera shouted at the neighbours, according to the report. He then shouted, "everything is okay."
He took off running when he saw the neighbours were on the phone, the report said.
Delray Beach Police found Rivera about 7 a.m., the report said. He spontaneously uttered "I killed my sisters," according to the report.
He was taken to the Boynton Beach Police Department, where he gave police a statement, and admitted to stabbing his sisters, the report said. He told investigators he used a brass knuckle knife to stab his sisters because a "higher power" told him it was "his purpose," the report said.
UFC officials released a statement to MMA Weekly, a digital publication that covers the profession.
"UFC is aware of the recent incident involving Irwin Rivera and subsequently received information from his management that he has been exhibiting behaviour consistent with mental health issues," the statement said. The statement said Rivera's career is on hold pending an investigation.
A lawyer for Rivera was not listed on jail records.