DETROIT -- An armored truck lost a bin full of cash around 8:30 a.m. Thursday, spilling bills all over the southbound lanes of Interstate 75 just north of Clay Road.

"It's exhilarating. It's not mine but it's still. I don't know. I can't explain it," said Marlene Stevenson as she watched police and Loomis employees pick up the money.

Police had the far lanes of the freeway blocked for several hours during the morning rush while they worked to clean up the cash.

The driver and the armed guard who sits in the back with the money immediately pulled over when they realized the money had flown out the back.

Investigators said they are trying to determine if a human error or a truck malfunction caused the back doors to fly open and spill the loot.

The money was picked up from the freeway and all lanes have reopened.

According to the Michigan State Police, $160,000 is still missing. Loomis, the Texas-based armored truck company, is offering a ten percent reward, no questions asked, for anyone who returns money.

Police are also looking at surveillance video from cameras mounted along I-75, in hopes of figuring out who took the cash.

"Any monies that are lost are obviously guaranteed by Loomis to the people who own them," said Loomis spokesman Pat Flaharty.

One driver told Local 4 that police were picking up the cash, otherwise she might have tried to pick up some bills.

Another man told Local 4 that a family member told him about the cash on the freeway and he drove over to the area to see for himself.