ANAHEIM (CBSLA)  — Authorities have announced the arrest of a 21-year-old Anaheim man they said sexually assaulted a 12-year-old girl he met on a dating app.

Sex crimes detectives from Santa Ana Police surprised Sean Rickard and arrested him behind a shopping center Wednesday night.

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He believed he was meeting the girl who allegedly admitted to him she was a 7th grader and only 12. At first, she reportedly posted an online profile saying she was 19.

Rickard and the girl “met” first on Tinder, police said. They also interacted on Snapchat, officials said.

Rickard’s next-door-neighbor Maria Aguilar, told CBS2’s Michele Gile that the arrest doesn’t fit the young man she knows.

“I’m in shock, you know, I’m in shock,” Aguilar says. “Because I don’t know what’s going on.”

She told Gile that Rickard has always been friendly and kind.

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“I always see him always driving, or with his dad, and the parents,” she says. “To me he was this great kid, a great kid. They’re a great family.”

The online relationship between Rickard and the girl police say began eight months ago. The Santa Ana girl was spotted getting into Rickard’s car Monday and that’s when detectives were told about the pair.

“When he picked her up in the area of school,” says Santa Ana Police Department Cpl. Anthony Bertagna, “thankfully, another student saw it. Was not comfortable with it, took a picture. Went to their parents and told them what they saw. And that parent was astute enough to reach out to the school who did their job and contacted us.”

Gile met briefly with the suspect’s father in front of the Rickard family home. He told Gile he knew nothing about the accusations and walked away visibly stunned.

Officers told Gile that the girl who lied about her age looks “much” younger than 12, not older. They said she looked more like an elementary school student.

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Police said it’s a good time to remind parents to monitor what their kids are doing on line.