Metro detectives said they received a tip Monday from 18-year-old Elizabeth Morales, who said she might know something about Otremba's disappearance.
Morales said her boyfriend, 19-year-old Daniel Ortiz, received several phone calls from Righetti on Friday night, according to the arrest report.
"Ortiz told Morales that Righetti was upset and wanted Ortiz to come help him," police wrote in the report. "Ortiz said she couldn't come along because Righetti said she couldn't come and Ortiz said he was worried that Righetti had killed someone."
In an interview with detectives, Ortiz said he met Righetti at his house, where the latter confessed to committing several robberies and killing a young girl.
After purchasing gasoline and matches at an Albertson's Express store, Ortiz said he drove Righetti to the vacant lot near Grand Teton and Oso Blanca.
However, according to the arrest report, Ortiz did not follow Righetti to the body.
Detectives went to Righetti's house Monday, where he was placed in custody.
After being read his Miranda rights, police said Righetti admitted robbing, raping and stabbing Otremba with a kitchen knife from his house.
He also confessed to a second robbery and rape, according to the arrest report, although the details were not immediately made public.
Ortiz has not been charged in the case.
(pending identification).
