Authorities said employees at a 24 Hour Fitness called police after they said a member harassed several people.
Deputies with the Los Angeles County Sheriff's Department responded and said the man left, but later returned two hours later and began acting erratically in the parking lot.
"At one point became aggressive with a deputy and that deputy attempted to tase him. The Taser had no effect," Lt. Joe Mendoza with the Los Angeles County Sheriff's Department said.
The man threatened deputies with an electronic device with a tethered cord on it, according to officials.
"He began to swing it over his head toward the deputies. He was tased again and it was ineffective," Mendoza stated.
A deputy fired at least one round, striking and killing the man. The man, who was in his 40s, has not yet been identified by authorities.
Earl Ofari Hutchinson, the president of the Los Angeles Urban Policy Roundtable, said the death could have been prevented.
"In this case there's strong evidence that if you had a mentally trained health professional there it may have been preventable," Hutchinson said.
The sheriff's department has mental health evaluation teams that pair a deputy with a licensed mental health professional during a psychiatric crisis. It recently double the number of those teams to 10 and hopes to expand to 23.
Hutchinson said he wants to make sure those teams are being deployed when necessary.
"You have to have them on the scene," Hutchinson said. "When you do that the goal is to prevent the loss of life."
The sheriff's department released the following statement to Eyewitness:
"Deputies on scene called the Mental Evaluation Team once the suspect became uncooperative. On any given day, there are approximately two MET teams available to cover more than 4,000 square miles of Los Angeles County. Prior to the call to MDR (Marina del Rey), one MET team was responding in the Antelope Valley. The second team MET team was called to a different location, 15 miles away from MDR. It is estimated that the number of MET teams would have to more than triple in order to meet the number of calls for service that involve individuals suffering from mental illness."