( CNN ) -- In a soft voice , teenager Austin Sigg confessed in gruesome detail how he snatched a 10-year-old girl from his Colorado neighborhood and dismembered her . But what Sigg could not explain to police detectives is why . `` It was a random place , a random time . Random everything , '' Sigg told officers in interrogation video released this week . `` I was just driving and just kind of looking . And I saw her ... found the place to park . And I parked , and I waited . And she walked by , and I grabbed her . '' Sigg is going to have a lot of time to think about it . He was sentenced to life in prison last week . The tapes released this week by the Jefferson County District Attorney give a chilling look into Sigg 's thoughts . Sigg was 17 when he grabbed Jessica Ridgeway off the street in October 2012 . I told her everything would be OK. Sigg told police during the interrogation that he got her into his car . He tied her hands and legs together and drove around for 20 minutes as she frantically screamed and asked him questions . `` I would lie to her , '' Sigg said . `` I would tell her everything was going to be OK . I would just lie to her . '' He took the bespectacled , blond girl back to his house . What happened there may have been very graphic . Parts of the interrogation tape were redacted by authorities . Sigg made girls in the area uneasy . Eligible for parole . Sigg will be eligible for parole after 40 years for the murder . But a judge sentenced him to close to 100 additional years for the other charges against him . Along with Ridgeway 's murder , Sigg also confessed to the attack and attempted kidnapping on a jogger that occurred earlier in the year . Using all those charges against Sigg , the judge said he expects Sigg to be confined to a cell for the rest of his natural life . Turned in by his mother . Jessica Ridgeway was missing for five days and authorities were searching everywhere in October 2012 . The break in the case came after Sigg told his mother what he had done . His mother , police said , called 911 and handed the phone to her son . During the trial , Ridgeway 's family members were in court wearing the little girl 's favorite color , purple . `` This monster took away from me the light of my life , '' said Christine Ridgeway , Jessica 's grandmother . `` It shattered the core of my family . ''
Thomas Sigg confessed to killing , dismembering 10-year - old girl . He was 17 at the time . He was sentenced to life in the last week .