On March 16, 1990, Michael Steven Gallegos killed his 8 year old step-niece Kindall Wishon by holding his hand over her mouth and nose causing her to suffocate while he sexually assaulted her. 

After she died he then proceeded to have anal intercourse with her body while in her bedroom in Phoenix. 

He told police he went ahead and finished the act after she was dead because it wasn't like she was going to tell anybody.  The PSI mentions an accomplish named George Smallwood, but the County Attorney chose not to prosecute him for lack of evidence.

Inmate Gallegos was also convicted on May 24, 1991 of the following:

Maricopa County CR 90-03339 - Count 2 Sexual Conduct with a Minor, committed on 3/16/90, sentenced to 21 years flat, consecutive to Count 1.

PROCEEDINGS
    Presiding Judge: Jeffery A. Hotharn
    Prosecutor: Louis F. Stalzer
    Start of Trial: March 6, 1991
    Verdict: March 14, 1991
    Sentencing: May 24, 1991
    Resentencing: October 24, 1994

Aggravating Circumstances:
    Especially heinous/cruel/depraved
    Age of victim (8)

Mitigating Circumstances:
    Defendant's age (18)
    Remorse
    Recommendation of leniency by police
    History of alcohol and drug use
    Alcohol impairment (non-statutory)

PUBLISHED OPINIONS
    State v. Gallegos, 178 Ariz. 1, 870 P.2d 1097 (1994).
    State v. Gallegos, 185 Ariz. 340, 916 P.2d 1056 (1996).