A California father murdered his 5-year-old son after a trip to Disneyland to get back at his estranged wife after their bitter divorce, police allege.

Aramazd Andressian jnr has been missing for two months and his body has not been found.

But investigators said strong circumstantial evidence proved the boy was killed by his father, Aramazd Andressian snr, the Daily Mail reported.

The boy was last seen at Disneyland with his father on April 21. Photo / via Facebook
The boy was last seen at Disneyland with his father on April 21. Photo / via Facebook

"I am confident the evidence proves Mr Andressian committed this horrible crime," Los Angeles County District Attorney Jackie Lacey said.

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Investigators have been searching for the boy since his father was found passed out in his car in Arroyo Park, South Pasadena, on April 22.

Police say the father had taken prescription pills and was found doused in gasoline in what they say was an attempt to take his own life.

The boy was last seen leaving Disneyland with his father about 1am on April 21.

Investigators believe Andressian killed his son a short time later and then drove about 230km later that morning to Lake Cachuma in Santa Barbara County.

Sheriff's homicide detectives have searched the lake twice in the past few months, using dogs and a dive team.

Andressian, 35, was arrested on Friday by sheriff's homicide detectives and federal agents in Las Vegas because he was "becoming a flight risk", Los Angeles County Sheriff Jim McDonnell said.

He's being held in the city on US$10 million ($13.75m) bail.

Los Angeles County Sheriff's Department Homicide Bureau Capt. Christopher Bergner, centre, stands by a poster of Aramazd Andressian Jr in May. Photo / AP
Los Angeles County Sheriff's Department Homicide Bureau Capt. Christopher Bergner, centre, stands by a poster of Aramazd Andressian Jr in May. Photo / AP
Los Angeles County Sheriff and South Pasadena Police departments search a drain in the Arroyo Seco wash in South Pasadena for the missing 5-year-old. Photo / AP
Los Angeles County Sheriff and South Pasadena Police departments search a drain in the Arroyo Seco wash in South Pasadena for the missing 5-year-old. Photo / AP
In this photo released by the Los Angeles County Sheriff's Department, homicide detectives arrest Aramazd Andressian Sr. Photo / AP
In this photo released by the Los Angeles County Sheriff's Department, homicide detectives arrest Aramazd Andressian Sr. Photo / AP
Aramazd Andressian Sr. appears in court. Photo / AP
Aramazd Andressian Sr. appears in court. Photo / AP

Andressian changed his appearance and had been "socialising" while living out of a Las Vegas hotel for 47 days, conduct characterised as inconsistent with that of a grieving parent, said Sheriff's Lieutenant Joe Mendoza.

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In a picture released of Andressian being arrested, his hair appears to have been dyed blond.

Investigators also believe Andressian was planning to leave the US and flee to a country that does not have an extradition agreement with the US, Mendoza said. Officials declined to identify the country.

Detectives believe Andressian killed his son in an attempt to get back at his estranged wife for their "tumultuous" relationship, Mendoza said.

The couple were separated and had been sharing custody. The boy was last seen by his mother who had a video chat with him on April 18 as he visited with his father.

The boy's mother was scheduled to have a video chat with her son on April 20, but that never happened, said South Pasadena Police Chief Art Miller.

Police began investigating after Andressian failed to drop off the boy with his mother that weekend.

Andressian's attorney, Daniel Nardoni, has said his client "is adamant that he never harmed Aramazd and is innocent of the charges". Nardoni did not immediately respond to a request for comment.

Aramazd Andressian Sr. appears in court in Las Vegas, charged with the murder of his son. Photo / AP
Aramazd Andressian Sr. appears in court in Las Vegas, charged with the murder of his son. Photo / AP

Andressian is expected to appear in court in Las Vegas for an extradition hearing and will likely be brought back to Los Angeles by the end of the week, prosecutors said.

"My heart is shattered and I will miss my son immensely each and every second of every day for the rest of my life," the boy's mother, Ana Estevez, said.

- Daily Mail