San Francisco (CNN) -- The discovery of the body of a woman in a stairwell of San Francisco General Hospital weeks after she was reported missing from her room requires "a thorough, independent review," the mayor said Thursday.
The review will examine "top to bottom" the hospital's security and its systems controls as well as reporting procedures when a patient goes missing, Mayor Ed Lee said.
The announcement follows news this week that an engineering worker found the body of 57-year-old Lynne Spalding, who was reported missing on September 21, in the stairwell.
"It should have never happened, and on that we all agree," Lee said. "... I told the family, I wish to have all of the answers just as they do."
The review is expected to begin this week, he said.
Authorities have not released details about how Spalding died. She was admitted to the hospital on September 19 for a bladder infection. Her condition was improving when she disappeared two days later, according to the joint statement released this week by the hospital and sheriff's department.
"She was in fair condition when she left her hospital room shortly after being checked on by a nurse at 10:15 a.m. Fifteen minutes later, the nurse checked on her again, and upon finding her room empty, initiated a search of the hospital," the statement said.
Thirty minutes later after she disappeared, two of her friends and her boyfriend arrived at the hospital to visit, David Perry, a Spalding family spokesman. They were told that Spalding had been missing for 30 minutes, he said.
Hospital officials and police say they are investigating. The hospital says it has no idea how the body ended up in the rarely-used staircase.
According to the joint statement, when Spalding was not found, the hospital staff notified the family and sheriff's department officials on site. Deputies searched the campus, and did not find her.
Spalding's body was found Tuesday in the stairwell by a member of the hospital's engineering staff who was conducting a routine quarterly check, according to the statement.
"The exterior stairwell is a fire exit that is not routinely used by staff, patients or the public. It is alarmed and locks from the outside; it exits to the hospital grounds at the bottom," it said.
Chelsea J. Carter wrote and reported from Atlanta, and Dan Simon reported from San Francisco. CNN's Lateef Mungin contributed to this report.