SAN DIEGO -- An Army reservist from Serra Mesa who worked for San Diego County for two decades was among the 13 people killed in Thursday's shooting rampage at a Texas military base, a county official said Friday.

John Gaffaney, 56, who was a psychiatric nurse by training, most recently served as a supervisor for the county Adult Protective Services Department, according to Ellen Schmeding, assistant deputy director of the county Aging and Independence Services Department.

The Pentagon has not released a list of the victims yet, but Schmeding sent an e-mail Friday saying Gaffaney had been killed in the massacre at Fort Hood.

Gaffaney had traveled to Fort Hood just this week to prepare for a yearlong overseas deployment, according to county officials.

In his civilian job with the county, Gaffaney helped elderly victims of abuse and neglect, Schmeding said.

The husband and father of a grown son previously had been with the county Mental Health Services Department.

Before working for the county, he been in the Army, earning the rank of major, Schmeding said.

Gaffaney was enthusiastic about his military-reservist role and "really felt he could make a difference" serving armed-forces personnel, Schmeding said.

His county colleagues were stunned to learn of his death Thursday evening, she said.

"Everybody is quite shocked and shook up over what happened," Schmeding said, adding that Gaffaney will be "sorely missed."

In all, 13 people were killed when a gunman -- identified by military authorities as Army Major Nidal Malik Hasan -- opened fire Thursday in a packed health-services building at Fort Hood, the largest military base in the United States. Thirty-one others, including Hasan, were wounded in the rampage.

Hasan, a 39-year-old military psychiatrist, was born in the United States, but is a Muslim of Palestinian descent.

Authorities have not released a motive for the attack, but media outlets have reported Hasan was upset about being deployed to Iraq. He had reportedly been disciplined in the past for proselytizing, and had been harassed by his peers for his religion, especially after the Sept. 11, 2001, terrorist attacks.

As a psychiatrist, he worked with soldiers traumatized by their war experiences.

After opening fire, he was shot multiple times by a female civilian police officer. He is expected to live but has been in a coma, and authorities have been unable to question him.

The police officer is reportedly in stable condition and expected to survive, although some of the other wounded victims may not, according to media reports.