(CNN) Vanessa Marquez, an actress best known for her recurring role as a nurse on the NBC drama "ER," was shot and killed by police in South Pasadena, California on Thursday, according to the Los Angeles County Sheriff's Department.

Police were called to the 1100 Block of Fremont Avenue in South Pasadena just before 2 p.m. local time on Thursday to perform a welfare check. Upon arrival, Marquez, 49, was having seizures and appeared to be suffering from mental issues, officials told CNN.

After about 90-minutes of trying to offer Marquez medical help, police said she armed herself with what appeared to be a handgun and police opened fire.

The weapon turned out to be a BB gun, investigators said.

Marquez played nurse Wendy Goldman on "ER" for three seasons, from 1994-97. Though her character never had major storylines, she was sometimes involved in episode subplots, some of which had a light-hearted bent.

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