Mendonza said Andressian Sr. and his son, Aramazd Andressian Jr., were last seen leaving Disneyland in Anaheim at about 1 in the morning on April 21, the day before the boy went missing.
The father's attorney, Robert Nardoni, has previously said his client is innocent and that last week's arrest came as a surprise.
Aramazd Andressian, 35, was booked Friday afternoon on $10 million bail at the Clark County Detention Center on an out-of-state murder warrant, Metro said.
He is being held in a Las Vegas jail pending his extradition to Los Angeles, McDonnell said. Aramazd Andressian Jr. has been missing for more than two months despite an extensive search by investigators that reached from his hometown to Santa Barbara.
Although the boy's body has not been found, detectives and the D.A.'s office believe there is enough evidence for a conviction.
Andressian was in the middle of a divorce and custody battle with the boy's mother, Ana Estevez, who investigators have said is not a suspect in the child's disappearance.
Andressian told police that he had taken prescription drugs that didn't belong to him earlier in the morning of April 22. Jackie Lacey said her office has successfully prosecuted murder cases without a body and that she was confident there was strong evidence that Andressian "committed this awful crime".
The California father of a missing 5-year-old boy has been arrested in Las Vegas and is suspected in the boy's death. The boy's father had reportedly recently moved into the home, where investigators "seized various items of evidence", according to a sheriff's statement released at the time. The sheriff's department plans to release more information on Monday during a news conference. Police have alleged that the inside of his auto was doused with gasoline and there were matches in his vehicle.
Andressian Jr. was reported missing by his mother on April 22 when Andressian Sr. failed to turn over the child to his mother for a scheduled custody exchange.
In a statement shared by the Sheriff's Department, Estevez thanked investigators and the community for all the concern they've shown for her son, who goes by the nickname "Piqui".
Estevez has also spoken publicly, pleading for the public's help at a May news conference with law enforcement.
"My heart is shattered and I will miss my son immensely each and every second of every day for the rest of my life", she said in the statement. The boy was first reported missing by his mother when her estranged husband didn't bring him home at the agreed upon time. I'm counting the days until I see you again.
Anyone with information on the case is asked to contact the sheriff's Homicide Bureau at 323-890-5500.