Mittelsteadt was found by Reno police on March 6, lying in the 1000 block of Forest Street. He appeared to have been beaten and had several stab wounds.
Mittelsteadt was rushed Renown Regional medical Center where he died.
After an investigation, Cox was arrested on Friday and charged with murder with the use of a deadly weapon.
No bail was set.
Detectives are asking to speak with anyone who may have any knowledge of the homicide or the events that led up to it.
Anyone with information is encouraged to contact the Reno Police Department Robbery / Homicide Unit at 334-2188 or remain anonymous by contacting Secret Witness at 322-4900.