BOZEMAN, Mont. -

A convicted sex offender who had been arrested on suspicion of assaulting and trying to rape his former girlfriend in Bozeman is now charged with failing to register as a sex offender during the three weeks between his escape from police and his Feb. 21 arrest in Portland, Ore.

The Bozeman Daily Chronicle reports Gallatin County prosecutors filed the felony charge against 28-year-old Kevin Anthony Briggs on Monday.

Briggs was required to register his address after being convicted of kidnapping and raping his 14-year-old former girlfriend when he was 16.

Bozeman police arrested Briggs early on Feb. 1 after his former girlfriend reported an assault. Prosecutors say he walked out of an unlocked interview room during a shift change.

Briggs also is charged with aggravated assault, attempted sexual intercourse without consent, assault on a peace officer and escape.