Amber Marshall was a mom on a mission Tuesday, searching for her 8-year-old son Jack's bike that had been stolen off the family's front porch.

She not only found it, but she and her husband, Eric, also uncovered what appeared to be a chop-shop for stolen bicycles in the heart of Duluth's Lincoln Park neighborhood - a garage full of 20 or so bikes in various states of disassembly.

"We left his bike out on the front porch overnight. ... It was still there when he left for school. But at about 11 my husband called me to say Jack's bike was gone,'' Amber Marshall told the News Tribune. "I couldn't believe someone would walk up there and do that in broad daylight."

Marshall was so upset that she left work in downtown Duluth to search their Lincoln Park neighborhood. Eric searched, too, and so did their teenage daughter, Lexi. They drove through most of the neighborhood's streets and alleys looking for the dark blue BMX-style bike.

"You have to understand that Jack saved up all his Christmas money and all his birthday money to go down to Stewart's bike shop to buy this bike on his own,'' she said. "This bike is a big deal to him."

Amber Marshall eventually had to go back to work.

"We called the police and they sent an officer out to take the report, which was great," Eric Marshall said. "But he told us not to expect much. He said the bike was probably already repainted, or in pieces. He said they don't normally recover stolen bikes."

Eric Marshall said he looked for more than four hours before giving up.

But, on her way home from work Tuesday evening, Amber Marshall noticed two teenage boys riding across 24th Avenue West on bikes. She recognized one of the bikes as Jack's.

"I don't normally take that route home, but my friend called to say she needed a ride home from her job at the mall, so it was very lucky," Amber Marshall said. "I said, holy... that's Jack's bike! It was a pretty big teenager riding an 8-year-old's bike."

She followed the teenagers to a home on the 2300 block of West Fourth Street, where they ditched the bike in the front yard.

"I didn't know what to do. I had my friend and her son with me. ... So I took them home and came back," she said.

The bike was still in the yard, but so was a woman and one of the teenagers she had seen riding minutes earlier. The bike had a reflector in an unusual place and a Stewart's sticker in a specific place. There was no doubt it was Jack's bike, she said.

"I didn't think I could just take it without saying something. So I asked if they happened to see a blue bike, which was sitting right there. ... The woman told me to just take it. It's like she knew it was stolen. The teenager tried to say it was his, but I kind of got in his face and told him he was lying," Amber Marshall said.

Amber Marshall said the woman, apparently the teenager's grandmother, asked her to call the police and that the woman essentially admitted her grandson had been stealing bikes.

As Amber Marshall was dialing 911, the teenagers and an adult male left in a large van. They apparently were moving out, Marshall said.

"I think I just got there in time. I think they would have taken Jack's bike with them," she said.

As a police officer arrived, Eric Marshall drove through the alley where he saw a mess of bikes and bike parts in the garage, and in the backyard "there were bikes all around," he said. "There were parts of maybe 20 or 30 bikes, but it was hard to tell exactly."

Eric Marshall said the officer lined several bikes up outside the garage, taking photos and attempting to get serial numbers to match with any bikes reported stolen. Jack's bike already had scratch marks where the culprits tried to remove stickers, as well as some new parts added, only hours after it was stolen.

"'It seems like everyone at the house knew what was going on, but nobody did anything until we stumbled into our son's bike," Eric Marshall said.

The Marshalls credit Duluth police with fast action, but said the officers had few options because the teenagers had already left.

"They took it very seriously. They did their jobs," Eric said of the police efforts.

Amber Marshall said the woman at the house told the Marshalls to put the word out for anyone who was missing a bike in the Lincoln Park neighborhood to come over and look in the garage. The Marshalls took a photo of a lineup of bikes that they posted on Facebook.

"But the bikes were so parted out, and painted, and just in pieces. ... There wasn't much left of any one bike,'' Eric said. "I don't know what they were doing with them - maybe using the parts to make superbikes and selling them? There were a lot of broken hearts piled in that garage."

Duluth police spokesman Ron Tinsley confirmed Wednesday that police responded to the 2300 block of West Fourth Street but said that the investigation into bikes discovered there is not complete.

Tinsley encouraged people to report any stolen bike, as the Marshalls did. But unless the bike is unusual or the owner has a photo or an accurate serial number, Tinsley said they can't be easily identified even if they are recovered.

"We want people to call. But most people don't. Most people don't think there's anything they can do," Tinsley said. "It's great to have identifying characteristics so you can go on social media and ask people, have you see my bike?"

On Wednesday several bikes remained outside the still-open garage. The bikes appeared to have dissimilar parts connected; some were spraypainted.

A young boy in the alley Wednesday who said he lives in the neighborhood said he had helped the teenagers build bikes in the garage, but that the teens had moved away. When asked where the teens got all the bikes, the young boy said they found them or bought them.

The Marshalls said Wednesday that they doubted anyone else would find their intact bike in the cache in the alley behind West Fourth Street, or that anyone would ever be prosecuted. Some friends and neighbors already had checked to see if their missing bike was in the mix.

So far, Amber said, no one found the bike they were looking for.

"But we got Jack's back,'' Amber said as she watched Jack take a spin down the sidewalk. "So we made one kid very happy."