SUNNYVALE — When someone hurriedly got into a stranger's running SUV at a Sunnyvale motel and drove off, prompting a middle-of-the-night Amber Alert that startled millions of Bay Area residents out of their slumber, police had an idea of who might have been behind it.

But in the hectic aftermath of the abduction, there was no clear evidence from the North Mathilda Avenue motel of who took the 2-year-old boy. He had been sleeping in the back of the 2018 Buick Enclave and was taken in a brief moment Sunday when his mother was away, unloading groceries from the vehicle to their room.

Early on, investigators put out a news release that named 29-year-old Luong "Tammy" Huynh as someone who "may have information that will help us locate" the child, but stopped short of revealing what they believed her role to be. She was arrested Sunday night.

"We had strong suspicions she might be involved, but we didn't have actual video of her getting into the car and taking off," Capt. Craig Anderson of the Sunnyvale Department of Public Safety said in an interview Monday.

After that 3:51 a.m. Amber Alert, the day dragged on in agony as the boy's mother pleaded with the public to keep their eyes peeled, and the FBI quickly got involved by offering a reward to whoever could lead authorities to the child. Around 6 p.m., Sunnyvale authorities announced that they found the boy safe in the Buick, which was now parked about three miles east of the motel in a thinly populated office park off Oakmead Parkway.

And there was better surveillance video there, which investigators say strongly identified Huynh as the likely culprit.

"After finding the kid and reuniting him with his mom, officers were doing another canvas of area where car was found, and they got additional video of Tammy in and around the car," Anderson said.

Anderson added that as they were confirming Huynh's involvement, someone at a San Jose address associated with her — one of several that detectives visited over the course of the day — called police to tell them she had just arrived.

Within a couple of hours of the SUV being found, San Jose police were dispatched to a Florence Avenue home to detain Huynh, and Sunnyvale investigators soon followed to arrest her. Huynh was booked into jail on suspicion of kidnapping, child endangerment, and auto theft, authorities said.

Anderson said there is no connection between the boy and his mother and Huynh, other than that they were staying at the Sunnyvale motel at the same time. He also said during a police interrogation, Huynh told detectives that she was visiting someone at the motel and abruptly decided to leave, and saw an unattended, running SUV as her chance to get away.

She reportedly told police that she did not know the toddler was inside, and drove to the Oakmead Parkway site, parked, then slept in the vehicle before abandoning it and the child. Anderson said Huynh appears to have ditched the SUV because it wouldn't run, likely from not having enough fuel.

The boy's mother, Melissa Jardine, 29, said Sunday that her child and car vanished in a flash.

"Before I even got out of my room, I heard a car squeal, and as I came out here, he was gone, the car was gone, everybody was gone," she said.

Jardine said she called 911, then drove another car to the tops of parking garages to peer out over the city in a hope to spot the car, which had a distinctive travel bag on top of it. Within hours, the FBI, Santa Clara County Sheriff's Office, SJPD and the California Highway Patrol were joining Sunnyvale authorities in the search for the boy.

Anderson said authorities received no tips in response to the Amber Alert, but he suspects that could be because by the time it was issued, Huynh was no longer on the move and had parked in a commercial zone that sees minimal traffic on the weekend.

Staff writers Jakob Rodgers and George Kelly contributed to this report.