In announcing that Christian Birdsall, 16, and Cody Nicosia, 18, were arrested on Thursday in connection with the killing of 58-year-old Barbara Latiolais, Nelson said, "These two are evil to do something like this."
Joining Nelson at a news conference at a substation in San Leandro, Sgt. Dave Dickson said, "I've been doing this for 29 years and this is the most callous crime I've ever been associated with."
Latiolais' body was found at about 12:15 a.m. on Oct. 18 after the house in the 2400 block of San Carlos Avenue was set on fire, Nelson said.
He said an investigation determined that Birdsall was a distant relative of Latiolais' boyfriend, retired San Francisco firefighter Michael Rice, who owns the house, and that Birdsall had done some yard work for the couple.
Birdsall and Nicosia wanted to steal guns and money from the house and planned their crime for Oct. 17 because they knew Rice was out of the state, Nelson said.
Dickson said they arrived at around 8 a.m. and waited for four to five hours for Latiolais to leave, but when she continued to stay in the house, they decided to go inside and "made the decision to kill her."
Nelson said Nicosia grabbed Latiolais from behind and choked her to make her pass out and then he joined Birdsall in taking guns, money and jewelry from the house.
Latiolais later made a noise, so the two teens took a rope and strangled her to death, he said.
Birdsall then drove off with the loot in the couple's Volvo and had a late lunch at a local restaurant, according to Nelson.
Nelson said Birdsall and Nicosia later realized that "they left a dead body and evidence behind" so they returned to the home at about 10:30 p.m. that night to set the house on fire in an attempt to cover up evidence in the case.
Nelson said the crime was "a despicable act" because Latiolais "was in the sanctity of her own home but was violated by someone she knows and trusted."
Dixon said Rice "is absolutely devastated by this situation" and "broke down and started crying" when he was told all of the details of the crime.
He said Latiolais is survived by a daughter, a sister and several nieces.
Birdsall and Nicosia are scheduled to be arraigned this afternoon at the Hayward Hall of Justice, Alameda County prosecutors said.