LOS ANGELES -- A missing 5-year-old boy's father has been released from jail in an unexpected twist that only deepens the mystery behind the boy's disappearance.

Investigators on Tuesday decided against presenting the case to prosecutors and moving forward with charges against Aramazd Andressian Sr., who had been found unconscious Saturday at a South Pasadena park with his son Armazd Andressian Jr. nowhere to be found.

Andressian Sr., who is in a custody fight with the boy's mother, was vague and evasive in his answers to detectives' questions. He was arrested later Saturday on suspicion of child endangerment and abduction and was being held on $10 million bail before his release.

Authorities would say only that the investigation was continuing, and would not say whether the father remains a suspect.

Andressian and his family are "emotionally reeling" as investigators continue their search to find the boy and are hoping for his safe return, the father's attorney, Rebecca Lizarraga, said in a statement.

"Aramazd, his family and counsel are fully co-operating with the police in their efforts to locate little Ara," Lizarraga said.

Four days of intensive searching for the boy have yielded very little.

On Tuesday, authorities searched Cachuma Lake in Santa Barbara County where Andressian's car had been seen before his arrest, but later found surveillance video that showed the father had been there without his son.

Investigators have said the boy was last seen on April 18 during a video chat with his mother but they have so far been unable to identify precisely when he went missing.

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

Police began investigating after the mother reported that her estranged husband failed to drop the boy off at a pre-arranged meeting place Saturday. The parents are divorcing and share custody.

Investigators don't know why Andressian Sr. was unconscious at the park, but have said there is no evidence he was attacked.

His car was spotted a day earlier in Orange County and investigators believe he drove to Cachuma Lake -- about 193 kilometres northwest of Los Angeles -- and spent the day there.