Police officers didn't attempt any "lower levels of force" before one of them opened fire and killed an unarmed 73-year-old California man with dementia — even though the man made no apparent threatening moves toward them, officials said Tuesday evening.

Officer Reagan Selman, a member of the Bakersfield force since July 2015, fired seven rounds at the man, Francisco Serna, early Monday shortly after midnight, Assistant Police Chief Lyle Martin told reporters.

Serna, a father of five, grandfather of 16 and great-grandfather of five, died at the scene, he said.

Related: Family Blasts Police Shooting of Francisco Serna, Unarmed Senior

Martin, who will become chief of police on Wednesday, called the shooting a "tragedy" and said he extended his deepest condolences to Serna's family. Selman and six other officers are on routine administrative leave pending the investigation, he said.

Francisco Serna in a family photo. Courtesy of Serna family

The incident unfolded as Selman and the other officers were responding to 911 calls about an alleged man with a gun who was wandering the neighborhood and approaching women on the street in a "bizarre" manner, Martin said.

The officers were interviewing a neighbor when she suddenly blurted out: "That's him!" Martin said. When the officers turned around, Serna was approaching with his hands in his pockets, he said.

artin said Serna failed to comply with officers' orders to stop and show his hands.

"No lower levels of force were attempted by any officer" before Selman opened fire, he said.

Serna appeared to have made no "lunging" or otherwise threatening movement toward the officers, and no weapon was found at the scene, Martin said. But he said the "totality of the situation" was more complicated than it might seem.

Francisco Serna in a family photo. Courtesy of Serna family

Only 20 to 30 seconds elapsed "from the subject saying 'That's him!' to shots fired," Martin said. "They're being told he had a handgun and 'that's him.' It's kind of tough to address that in 20 seconds."

Serna's daughter Laura told NBC News earlier Tuesday that her father was diagnosed with dementia in July and that his health had taken a recent turn for the worse.

"My dad was murdered, I believe, for no reason," said Laura Serna, who lives in the same home, where a vigil was being held Tuesday night.

Martin said police were staying out of sight in the neighborhood unless they were needed.

"This is a tragedy," Martin said. "This is a very delicate situation. We respect the Serna family and their right to grieve."

At a vigil Tuesday night, the family through a friend thanked the community for its support. "The amount of the community that has come out this evening has really touched the hearts of the family," Cyndi Imperial said.