A former Marine who survived three tours in Iraq and a knife assault five months ago has been murdered in a mysterious attack while installing cable TV in a California home, police say.

Authorities said they don't know why a man inside the home where 25-year-old Trevor Neiman was working Monday grabbed a hammer and fatally beat the war veteran-turned-cable technician, The Los Angeles Times reported.

"There was no exchange of words. There was nothing that occurred before the unprovoked attack," San Bernardino County Sheriff's Department spokeswoman Jody Miller told the press.

Police said the alleged attacker, 45-year-old Johnny Acosta, initially fled the home, believed to belong to some of his relatives, but later turned himself in, the Times reported.

Casie Barnard, Neiman's 26-year-old sister, told the Times that Neiman was trying to build a life after serving in Iraq from October 2003 to 2008, recently getting married and buying a house in May.

That same month, someone attacked Neiman with a knife during a party at his home. The attack left him with broken ribs, a punctured lung and a severe head wound.

Police arrested three people on suspicion of attempted murder in that attack, the Times reported.

"When he came home from Iraq, we thought, 'Oh, OK,' he got home safe," Barnard said. "We don't have to worry."

Acosta his being held without bail on suspicion of murder and is set to appear in court Thursday, the Times reported.

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