A woman who went on a suicidal rampage inside a mail processing plant, killing six employees, may also have killed a former neighbor shortly before the attack, sheriff's officials said Wednesday.

The sixth employee, who had been hospitalized in critical condition, died Wednesday morning.

A possible seventh victim was found dead Tuesday from a gunshot wound to the head at a Santa Barbara condominium complex where the shooter, former postal employee Jennifer Sanmarco, once lived, said Lt. Jeff Klapakis, of the Santa Barbara County sheriff's department.

Klapakis said the victim, identified by her brother as Beverly Graham, 54, died on Monday.

"We are investigating it as being the beginning of this rampage," said sheriff's Sgt. Erik Raney.

Raney said a neighbor reported hearing a gunshot about 8:20 p.m. Monday.

About half an hour later, authorities said, Sanmarco fatally shot six postal employees at the Goleta mail processing plant before committing suicide in what is believed to be the deadliest workplace shooting by a woman.

U.S. Postal Inspector Randy DeGasperin said "chances are" she knew the people she was shooting.

DeGasperin said Sanmarco had left the mail facility on a medical leave in 2003 after her co-workers expressed concerns she might hurt herself. He said police removed her from the building one time.

"She was not making any threats or anything of that nature," DeGasperin said. "It was more for her safety."

Interviews with authorities in this picturesque coastal community and with people in New Mexico, where Sanmarco moved in 2004, paint a picture of a woman who exhibited increasingly bizarre behavior after losing her job.

"We weren't sure what she was going to do next," said Terri Gallegos, deputy clerk for the city of Milan, N.M., where Sanmarco applied for a business license in 2004 for a publication called "The Racist Press" that she said she planned to launch. Another time she said she wanted to register a cat food business.

During one meeting, Gallegos said, Sanmarco carried on a conversation with herself "like she was arguing with someone but there was no one there."

Last March, office workers called authorities after the 44-year-old woman made what Gallegos described as a rude allegation. Other times, Gallegos said, Sanmarco would come in and simply stare at one employee in particular.

In June, police in nearby Grants talked to her after someone at a gas station called to complain of nudity, Police Chief Marty Vigil said. Sanmarco was dressed when officers arrived.

Graham had also noticed unusual behavior, her brother Les Graham told The Associated Press.

He said his sister had complained about a woman who "used to come out and rant and rave in front of her building." The family suspects that Sanmarco was the neighbor and his sister's killer, he said.

Monday night, Sanmarco entered the sprawling Santa Barbara Processing and Distribution Center by driving through a gate behind another car, police said. She gained entry to the building by taking an employee's identification badge at gunpoint. That worker was not hurt.

Only about 80 of the approximately 300 people who work at the mail-sorting center were there when Sanmarco arrived.

"According to witnesses from the scene, she had a 9 mm pistol and reloaded at least once during her rampage," said Santa Barbara County Sheriff James Anderson.

Killed were Ze Fairchild, 37, and Maleka Higgins, 28, both of Santa Barbara; Nicola Grant, 42, and Guadalupe Swartz, 52, both of Lompoc; and Dexter Shannon, 57, of Oxnard.

Charlotte Colton, 44, of Santa Barbara died of her injuries Wednesday morning, said Teresa Rounds, spokeswoman for Santa Barbara Cottage Hospital.

Higgins had just returned from maternity leave. "She was a talker. There was not a moment she was quiet," colleague and friend Lexi Bushnell told the Santa Barbara News-Press. "She loved to lighten things up."

Swartz was emerging from a dark period after losing her husband, Donald, three years ago to cancer, according to friend Darlene Skura. "She was becoming more active, starting to get on with her life," Skura told the Los Angeles Times in Wednesday's editions.

Grant's neighbors said it was not uncommon to see the married mother of two shooting hoops with her children. "She was such a joy," said friend and neighbor Leslie Brown. "When you talked to her, she just glowed."

It was the deadliest shooting at any workplace since 2003, when 48-year-old Doug Williams gunned down 14 co-workers, killing six, at a Lockheed Martin aircraft parts plant in Meridian, Miss., before turning the gun on himself.

It was the first lethal shooting at a postal installation in nearly eight years and one of the deadliest since a string of high-profile cases in the 1980s and '90s — including one in which a part-time letter carrier killed 14 people in Edmond, Okla., before taking his own life.

James Alan Fox, a criminologist at Northeastern University, said he believed it might be the deadliest workplace shooting ever carried out by a woman.

"Men, more than women, tend to view their self-worth by what they do" at work, Fox said. Men also are more prone to use violence in seeking revenge while "women tend to view murder as a last resort," he said.

According to federal statistics, 12.3 percent of homicides are committed by women.