26-year-old Michele Le disappeared shortly after 7 p.m. when she took a break from her hospital rounds. Friends and witnesses told police she took her car keys and cell phone with her.
Police found her car on Ponderosa Court the next day with valuables still locked inside.
Investigators traced her cell phone based on tower locations and found it had been in Oakland, Union City and Fremont. Police were unable to get more information.
"The reality is, it's a pretty large area," said Lt. Roger Keener with the Hayward Police Department. "We've had the helicopter fly over the area...we haven't found anything at all that leads us (in) one direction or another, that tells us this is a foul play incident or anything."
Police say Le's cell phone can no longer be tracked -- either the battery is dead, the cell phone is turned off or it is out of range.
As of Saturday night, police were still unsure as to whether a crime had occurred or not. Investigators continue to question her colleagues at Kaiser and her college classmates.
