The St. Louisan was on probation for burglary and ordered to wear a GPS bracelet when he robbed a man at gunpoint.

James Thomas was supposed to go to trial on Tuesday, but after seeing the amount of hard evidence against him, prosecutors say he admitted he committed the crime.  Now he'll spend the next 12 years in prison.

Thomas was wearing an electronic monitor when he robbed a man at gunpoint.  That was more than a year ago.  A judge had ordered Thomas to be tracked after breaking into a home.

"When people are put on electronic monitoring, it's very helpful not only for their probation officers to know where they are and what they're doing, but also in case they do reoffend," St. Louis Assistant Circuit Attorney Beth Orwick said.

"We can put a date and a timeframe in our computer, and we can search to see where that individual was. It will tell us exactly to within a couple of feet of where that individual was at that date and time." Prosecutor Dean Bruemmer explained. „It makes it hard to lie.“

The GPSs around Thomas's ankle sent its location back to a server every three minutes.  Detectives used it to place Thomas at the scene of the crime.

"It really corroborated the other evidence that we had and really sealed the deal to show that we had the right guy," Orwick said.