From the List of unidentified murder victims in the United States:
Union County Jane Doe
A woman between 17 and 21 died on 10 July 1991 in El Dorado, Arkansas.
The decedent used multiple names, including Cheryl Ann Wick (which she
used from a stolen identification card), Kelly Carr and Shannon Wiley.
She was known to have lived in various states prior to her death,
including Texas, where she apparently worked as a prostitute. Other
reports explain she had been arrested in the past, using several of
her aliases and had possibly been involved in a bank robbery on the
East Coast. She had been shot by her boyfriend who was convicted of
the murder but she remains unidentified.
St. Petersburg Jane Doe
A 11 to 20-year-old girl who was pushed in front of a vehicle in St.
Petersburg, Pinellas County, Florida, on 9 June 1973. Her wavy hair
was auburn and shoulder length; her eyes were a vibrant blue. She wore
two earrings in one ear, a piercing in her other ear had healed. She
wore a ring missing its stone as well as a multicolored gown and
purple tights. It is possible that she was a runaway; some believe she
was from North Carolina or Virginia, as she told many inconsistent
stories. The victim was known by many names when she was alive,
including Janice Marie Brock, Marie, Maria and Cindy. It is also
suspected that she was involved with a drug activity, which may have
been a reason for her murder. Although her murderer, Lawrence Dorn,
was convicted of her death, the girl currently remains
It appears that there are about a 100 currently unidentified murder victims in the US (that the wikipedia editors bothers to collect).
Given that there are ~ 15k homicides in the US annually, I don't think there is much statistical significance here: it is rare for a victim to remain unidentified and it is very rare for such a crime to be solved.