DENVER -- Changes are made after a 7NEWS investigation on sex offenders. We found that sex offenders don't register as required by law.

Attorney General Ken Salazar has made good on his promise.

He's turned up the heat on police all over the state if a sex offender fails to properly register. Salazar wants them behind bars.

Our 7NEWS investigation knocked on dozens of doors. If you go by addresses provided by police, sex offenders live in these houses.

Our investigation found reports filled with mistakes -- sex offenders not living at the address listed in police reports. Now the attorney general wants violators arrested.

"He's asking law enforcement to ratchet it up, make it more of a priority," Deputy Attorney General Ken Lane said.

In a letter to top cops all over Colorado, the attorney general detailed their responsibility to enforce the law.

Tony Kovaleski: With this letter, the attorney general is sending a message -- a strong message.

Ken Lane, Deputy Attorney General: Yes, and that message is the registration of sex offenders should become a priority in our communities for a public safety standpoint.

The penalty for violating the state's registration law has also changed. Before July 1 of this year it was only a misdemeanor. Now district attorneys can charge violators with a felony.