Guatemala is still failing to take action over the high number of murders of women and girls in the country, according to Amnesty International.
The main suspect in Maria Isabel's 2001 murder has yet to be located
The rights group said there has been little progress since June 2005, when it called on the authorities to act.
Up to 70% of murders of women are not investigated and no arrests are made in 97% of cases, Amnesty says.
It adds that some officials recognise how serious the problem is, but many still tend to blame the victims.
Amnesty's latest report cites police figures which show that 229 women and girls were killed in Guatemala in the first six months of 2006.
229 women killed so far in 2006
665 women and girls killed in 2005
Between 2002 and 2005, murders of women rose 63%, of men 45%
Source: Amnesty report: "No protection, no justice"
Many of the murders were exceptionally brutal, with the victims suffering sexual violence, mutilation and dismemberment.
Amnesty says that it knows of only two convictions out of 665 murders of women in 2005.
Among the cases highlighted in the report is that of Cristina Hernandez, who was forced into a car outside her home on 27 July 2005.
Her father tried in vain to give chase and then went to a police to report the abduction and to ask the officers to set up roadblocks.
Her father said the officers refused, arguing that girls often ran off with boyfriends and that they could not begin a search for 24 hours.
Claudina Velazquez's family say her killer knew he was unlikely to be caught
Cristina's body was found the next morning. She had been shot four times and bitten all over her body.
Her family, afraid for their safety, went into hiding. Her killers are still at large.
Amnesty says that in many cases, there is a failure to carry out even basic investigations, process the crime scene and preserve potential evidence.
Heavy case loads, lack of equipment and the shortage of police investigators mean that few cases are pursued vigorously.
Amnesty is calling on the Guatemalan authorities to improve the quality of criminal investigations, including providing more training for investigators.
It also says there should be more efforts to guarantee the safety of witnesses and family members, and to follow up reported abductions of women and girls.