Teresa Sanchez, 27, and her brother Omar Aquino, 24, were found shot to death the morning of June 28 in their Plymouth Street home.
Mountain View police spokeswoman Liz Wylie said it appears Sanchez had made a 911 call that was answered by a California Highway Patrol dispatcher at 3:54 a.m. The call, which was reporting a break-in, was lost before it was connected to Mountain View police.
The CHP dispatcher claimed the caller gave an address on "Clemon" Street, which is not a valid address in that city.
Dispatchers and officers, who had the Sanchez' phone number but not the address, were still investigating the call when they received reports of shots fired in the 1900 block of Plymouth Street at 4:53 a.m.
Responding officers found Sanchez and Aquino dead of gunshot wounds inside the home, Wylie said.
"We are following leads and tips at this point, the investigation is far from over," Wylie said Tuesday.
Sanchez's 8-year-old son was found unharmed and asleep in another room of the home. He is now being cared for by relatives.
It appears that several subjects entered the home and confronted the victims, and that an argument preceded the shooting, Wylie said. Investigators believe that one or both of the victims knew the suspects.
Robbery does not appear to be a motive and it is not clear whether the shooting was planned, Wylie said.
A large, dark-skinned male was seen leaving the home in a dark-colored sedan, police report.
Anyone with information about this case is asked to call investigators at (650) 903-6344.