AURORA, Ill. (CBS) — Aurora police hope evidence from a sport-utility vehicle will help them find a 6-year-old boy who has been missing for nearly three weeks.

Timmothy Pitzen has not been seen since May 13.

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The 2004 Ford Expedition belonged to his mother, Amy Fry-Pitzen, who committed suicide after going on an outing with her son. The van was found on May 14 in the parking lot of the Rockford motel where her body was found, police said.

The van was visibly dirty, and weeds were found under it, police said.

It has since been towed back to Aurora, and police have been taking samples of dirt and growth. The samples will be tested by geologists and other experts, and police hope they will provide clues about where the van traveled.

They hope the substances on the van will prove to be unique to certain areas in the Rock Falls, Sterling and Dixon areas in western Illinois, where Timmothy and his mother were last known to be together.

Police say Fry-Pitzen took Timmothy out of school on May 11. Over the next two days, the pair visited the Brookfield Zoo in Brookfield, the Key Lime Cove Resort in Gurnee, and the Kalahari Resort at Wisconsin Dells.

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Before going to the Brookfield Zoo on May 11, Amy dropped off her 2004 Ford Expedition SUV for repairs at a La Grange body shop. She and Timmothy were then taken to the zoo by a shop employee at around 10:00 a.m. The pair returned to pick up the vehicle at about 3:00 p.m., before heading to Gurnee where they stayed overnight.

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Amy and Timmothy then headed to the Dells on May 12 and stayed there until the following morning.

Security video released last week showed Timmothy with his mother at Wisconsin Dells on May 13, shortly before Fry-Pitzen committed suicide in the motel room.

Fry-Pitzen left a note saying Timmothy was in someone’s care, but she didn’t say who.

Police are still trying to determine the other areas Timmothy and his mother might have visited. Detectives believe they might have visited the Interstate 88 and 39 corridors, where phone calls were placed from Fry-Pitzen’s cell phone. Her last call was placed around 1:30 p.m. around five miles northwest of Sterling near Illinois Route 40, police said.

Police also have released photos that resemble toys Fry-Pitzen bought for her son. The toys, which have not been located, include an “Aquatic Rig” toy truck made by Wild Republic toys; what appear to be several coins or discs with depicting giraffes, lions, elephants and other wild animals; an Iris brand plastic craft case, a Hot Wheels toy race car starter set, and a tube of kids’ Crest toothpaste.

Police are asking land owners, residents, visitors to parks and other outdoor enthusiasts, to be on the lookout for the items as they have yet to be found.

Meanwhile, a cell phone, an I-Pass, and Timmothy’s Spider-Man backpack are missing from the van.

So far, police have not put together any solid leads in Timmothy’s disappearance. Fry-Pitzen’s three computers have provided no clues, nor have interviews police have conducted.

Timmothy is about 4 feet 2 inches tall and weighs around 70 pounds, with brown hair and brown eyes.

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Anyone with information on the case is asked to call Aurora Police at (630) 256-5500, or their local authorities by dialing 911.