The judges ruled that consuming alcohol before the incident made Ramon Sosa, 32, behave negligently and without criminal intention.
However, the prosecutor and the victim's family criticised the judgment.
"We can find no way to understand the reasoning of the court," prosecutor Eduardo Luis Rodriguez Trejo said.
He demanded for a sentence of 15 years in jail.
"This is not justice, this is injustice. You can't give the same sentence for killing someone as for stealing a bicycle," said the victim's father Juan Carlos Nahuelcar, who also intends to appeal the court's decision.
The judges took into account Sosa's statements to the psychiatrists.
Sosa told that he remembered what happened before and after killing Laura Nahuelcar, 22, in General Roca in Feb 2008 but not while he was attacking her.