(Reuters) - The dismembered remains of a Colorado woman missing since her husband was discovered dead last week have been found, and the couple's teenage grandson and girlfriend have been arrested in connection with the slayings, authorities said on Tuesday.
Police in Sterling, about 110 miles (177 km) northeast of Denver, said partial remains of Shirley Severance, 70, were found at a reservoir 18 miles (29 km) southwest of the farming town, and a second set located across the state line in Lorenzo, Nebraska.
Her husband, Charles Severance, also 70, was found dead inside the couple's home last week, with his wife missing.
Sterling Police Chief Tyson Kerr said on Tuesday the elderly couple's grandson and his girlfriend were arrested for the slayings after investigators found the missing woman's remains late on Monday.
Brendan Lee Johnson, 19, and Cassandra Ann Rieb, 18, are being held without bond in the Logan County jail on suspicion of first-degree murder as well as felony robbery, theft and forgery charges, police said.
"These are the charges they are being held on and not necessarily the formal charges," Kerr said in a statement. "In addition, some of these charges may be filed as crimes against an at-risk adult."
Agents from the Colorado Bureau of Investigation, Sterling police and the Logan County Sheriff's Office are processing the multiple crime scenes and the investigation is ongoing, he said.
Kerr said an autopsy will be performed on Shirley Severence this week. Police have not revealed the full autopsy results for her husband.
Logan County District Attorney Brittny Lewton said the judge in the case had issued a gag order and so she could not discuss how the couple was killed, or a possible motive.
The two teenagers will be advised of the charges at a court hearing on Wednesday, Lewton said.
(Editing by Daniel Wallis and Sandra Maler)