But on Friday, a friend of Keane's said he was a good, trustworthy man and the accusations reported had been extremely upsetting.
It's believed Keane was punched.
Police believed Keane had an altercation with two men who then left and went towards a boardwalk.
"He was left at the scene. The people escorting him away struck him and went back towards the party," Brown said.
Then somebody called a medic.
"Mr Keane was treated and released at the scene at his request," Brown said.
But about 10am on New Year's Day, he was seen near Mission Boulevard and Santa Barbara Place.
"Someone found him and thought he had overdosed," Brown added.
"The officers immediately recognised he had some sort of a head trauma."
He was taken to hospital.
"His head trauma was not survivable and that's when the homicide unit got involved," Brown added.
Keane died as a result of his injuries on January 8. His name was released yesterday, nearly a week later.
Detectives in San Diego collected evidence and interviewed witnesses.
"The investigation has been pretty much completed and it will be referred to the District Attorney's office for evaluation," Brown said.
The District Attorney's office will decide if anybody will be prosecuted for Keane's death.
Police in San Diego have been in contact with Keane's family.
The police said Keane had been visiting for work.
Some of Keane's friends have spoken on social media of their grief at his death.
Several people described him as a fun-loving man and good friend and said he would be sorely missed.
One man said it was very upsetting to think his friend died alone.
The Ministry of Foreign Affairs and Trade said it was providing consular assistance to Keane's family.