FORT COLLINS, Colo. -- (CNN) -- Tim Masters is no longer the slim, shaggy-haired 15-year-old he was when neighbor Peggy Hettrick was murdered, mutilated and dumped in a field near his home.

Tim Masters is serving a life sentence for a murder conviction that is now being questioned.

Goateed and bespectacled with a slightly receding hairline, Masters, now 36, sat quietly in a Fort Collins courtroom this week, occasionally flashing a boyish smile as his defense team worked to poke holes in his 1999 murder conviction, CNN.com reported Friday.

The conviction followed a 12-year investigation that Masters' defense attorneys say is flawed because it focused on building a case against a suspect instead of solving a murder.

Masters' attorneys want a judge to toss his murder conviction out and to grant him a new trial.

Defense attorneys said an FBI profile that played a key role in convicting him is missing from evidence. A forensic psychologist for the prosecution used the profile to create a theory that Masters killed Hettrick as part of a fantasy.

Masters was convicted in 1999 -- 12 years after the slaying -- on a circumstantial case that included a psychological analysis, violent pictures he had drawn, the fact that he lived 100 feet from where Hettrick's body was found, and that police said he had seen the body but didn't report it.

San Diego psychologist J. Reid Meloy quoted the FBI profile in a 247-page binder of notes that he used to build his psychological analysis.

Among his findings were that the killer could have planned the slaying to coincide with a "personally significant" anniversary. Hettrick died within a day or two of the anniversary of the death of Masters' mother, and Meloy noted that Hettrick, like Masters' mother, had red hair.

Other lost or destroyed pieces of evidence in the case include hairs found on Hettrick's footwear and photos of fingerprints from her purse, none of which match Masters.

Part of Masters' defense is that investigators may overlooked a potential suspect, an eye doctor who lived nearby and who had a sexual fetish. Dr. Richard Hammond committed suicide in 1995 immediately after police accused him of secretly videotaping the genitalia of female visitors who used the bathroom at his home.

Some of the wounds on Hettrick's body originally were described by the county's medical examiner as "surgical" in nature. Later that was changed to wounds of "mutilation" that could have been done by anyone with a knife and a desire.

Prosecutors said Hammond was home with his wife on Feb. 11, 1987, when Hettrick, a manager at Fort Collins Fashion Bar, was stabbed in the back and sexually mutilated.

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