San Francisco prosecutors have decided not to pursue a murder charge against the California man accused of the one punch killing of Australian tourist Matthew Bate.
David Murillo, a 34-year-old from Hesperia, north-east of Los Angeles, was arrested and booked into San Francisco County Jail for murder after Mr Bate suffered what police described as "severe head trauma" and was left unconscious outside the Da Vinci Villa Hotel about 2am local time on Friday.
After reviewing the case on Monday, District Attorney spokesman Alex Bastian told AAP Murillo was charged with three lesser felony counts: involuntary manslaughter; assault; and battery.
According to a source familiar with the investigation it appears words were exchanged between Murillo and Mr Bate and Murillo allegedly threw a single punch at the Australian.
Alcohol may have played a role in the incident and it is believed Murillo does not have a criminal record.
He is scheduled to appear in a San Francisco court for arraignment on Tuesday (6.30am Wednesday AEST).
Mr Bate, an analytical chemist and keen cricketer originally from Ocean Grove in Victoria who had recently lived in Darwin, was on a US holiday when tragedy struck in San Francisco's Russian Hill district, a popular place for bars where the closing time is 2am.
Police said they received a call at 2.18am regarding an unconscious man outside the Da Vinci Villa Hotel.
"Upon arrival, the officers found the victim, Mathew Bate, a 33-year-old Australian citizen, suffering from severe head trauma," police said in a statement.
"San Francisco Fire Department paramedics responded and rendered aid, but unfortunately Bate succumbed to his injuries at San Francisco General Hospital."
Police went door-to-door in the hotel immediately after the incident in search of Mr Bate's alleged attacker.
"Based on information and evidence immediately obtained at the scene, officers located and detained a possible suspect inside a hotel on the 2500 block of Van Ness Avenue," police said.
"San Francisco police homicide investigators were notified and began an investigation.
"At the conclusion of an interview with the detainee, it was determined this individual was responsible for Bate's murder."
Police will not release Murillo's mug shot "due to pending identification matters".
Witnesses or anyone with information on the incident have been asked to contact San Francisco Police anonymously.