He said Eduardo's three foster brothers and sisters, all around 9 or 10 years old, witnessed the incident and alerted an adult passer-by, who got a look at the car as it sped away.
Officers searching the area moments later found the car abandoned on the west side of Bergamont Park, according to Boyer.
A witness at the location told police Eduardo had been taken from the original vehicle and put into a "gold-ish or champagne Cadillac Escalade," Boyer said.
"This person saw the Escalade leave and go down Van Buren Boulevard, (east) toward Highway 215," the captain said. "The vehicle had paper or dealer plates, black and white with a series of numbers. They may be interstate transportation plates. We're not sure."
An all-points bulletin was broadcast on the Escalade, which had not been located as of late this afternoon. A statewide Amber Alert was also posted.
Boyer said investigators were scouring the first vehicle used in the abduction for clues. He said the last known owners of the car had been identified, but he would not disclose their names. Investigators were preparing to interview them.
In addition to the two men seen with the boy, a third man was spotted at the wheel of the Escalade. Police did not have a clear description of the suspects, other than that one of them was wearing a dark sweatshirt and jeans.
Boyer said Eduardo has been in foster care for the last several months, since his parents were arrested and jailed.
The boy's mother is in custody in Santa Ana for alleged identity theft, and the father is in San Bernardino County jail on similar charges, according to Boyer. Both parents are illegal immigrants and are being held without bail, he said.
Boyer said one scenario investigators are considering is that Eduardo's parents conspired to have their son taken from his foster family.
"We're not willing to say the parents have been exonerated from the investigation, though they clearly weren't active participants in the physical abduction," the captain said.
He said another possibility is the child was taken by people at odds with his mom and dad.
"It could be similar to what happened in Las Vegas just recently, where the kid is abducted because there are drugs involved," Boyer said. "We're all over the map right now... We're hoping for a good, honest statement (from Eduardo's parents)."
In October, 6-year-old Cole Puffinburger was abducted from his family's Las Vegas home by members of a Mexican drug cartel who barged in posing as police officers. The kidnapping may have been connected to a dispute over methamphetamine distribution allegedly involving Cole's grandfather. The boy was let go and found on a Las Vegas street a few days later.
Boyer said Riverside police have enlisted the help of the FBI to investigate Eduardo's abduction.
The boy is 3-foot-6 and 65 pounds, with brown eyes and hair. He was last seen wearing a dark-colored sweatshirt and blue jeans.
Anyone with information was urged to contact Riverside police at (951) 353-7137, or 911 if the child is spotted.
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