The army veteran who shot dead three women at a treatment centre struggled to adjust to life after returning from Afghanistan, according to his childhood guardian.
Albert Wong, 36, took hostages at a staff party at the Veterans Home of California, in Yountville, before killing the women and himself.
The victims of the Friday shooting were named as The Pathway Home executive director Christine Loeber, 48, clinical director Jennifer Golick, 42, and Jennifer Gonzales Shushereba, 32, a clinical psychologist with the San Francisco Department of Veterans Affairs Healthcare System.
There are reports that Mrs Shushereba was seven months pregnant and was due to travel to Washington DC to celebrate her wedding anniversary over the weekend.
Wong was an army rifleman who served a year in Afghanistan from 2011 to 2012, but is said to have struggled with returning to civilian life.
Cissy Sherr, his childhood legal guardian, said he had always wanted to join the army and hoped the Pathway Home programme would help him readjust when he left the military.
Wong was cared for by Mrs Sherr and her husband after his father died and his mother suffered ill health.
He then went into foster care as a teenager because the couple worked full-time.
She said: "He always had a great smile on his face.
"He didn't have a traditional upbringing but still he just became a fine young man. I can't imagine what happened. It doesn't make any sense to me."
Mrs Sherr said his skill as a marksman meant he carried out missions in Afghanistan that left him "anxious and wary" when he got back home.
She said: "I had the impression he was kind of put in harm's way, knowing that he didn't have a family. He didn't seem the least bit resentful."
She added that Wong was having trouble sleeping, and life after the army "started to catch up with him".
Mrs Sherr said: "A couple of years ago, he told us if a door opens unexpectedly, I ask, 'What is that?'"
"In less than a year – less than half a year – things started to unravel.
"He may have been without any resources to support him."
The three victims worked on The Pathway Home programme, which Wong had been on but was dismissed from. Officials have not confirmed why he was removed from the programme.
However, Ms Golick's father-in-law said she had ordered the veteran to be dismissed from the treatment course.
In a statement, T.J. Shushereba, Ms Shushereba's husband said she "will always be remembered for her unconditional love and incredibly giving heart".
It continued: "Jennifer and her colleagues died doing the work they were so passionate about – helping those in critical need."
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Yountville Mayor John Dubar said: "We lost three beautiful people yesterday. We also lost one of our heroes who clearly had demons that resulted in the terrible tragedy that we all experienced here."
President Donald Trump tweeted: "We are deeply saddened by the tragic situation in Yountville and mourn the loss of three incredible women who cared for our Veterans."