Just a copy-paste from a post I wrote back in 2008 (History board):
I've checked some books by Vucetich :
"Sistema de filiacion" (second edition, 1896) : Mostly about Anthropometry, a bit on fingerprints, doesn't mention the Rojas case
"Conferencia sobre el sistema dactiloscopico" (1901) :
Page 18
In 1892, the woman called Francisca Rojas, who lived in Necochea, killed two of her children without pity and declared to the police that the culprit was an honest neighbour. Commissionner Eduardo M. Alvarez, left La Plata to conduct the investigation. During his investigations, he found several finger marks on a door. He cut out the parts on which the marks were found. These parts are still kept at the depot.
After that, he took the fingerprints of the suspect and the woman who accused him. It turned out that the bloody finger marks matched the prints of the latter (1).
(1) Letter from inspector E.M. Alvarez to Juan Vucetich. June 1892
The moment has come to declare you right on the matter you talked to me about and which meant such a great deal to our chief Nuňez. I’m talking about finger prints, which served as a powerful means to demonstrate evidently who was the real culprit of a savage crime. Initially, an honest neighbour was being accused.
According the wishes of our chief, I write a telegram as follows : “Official, urgent : Do everything possible, even if you judge it to be unnecessary, to obtain finger marks left by the criminal and bring them with you. G.J. Nuňez.” I leave you two cards : the first one bears the fingerprints of the suspect at the time he was being suspected by the police. The second one bears the fingerprint of the one who finally was the only criminal. I also leave you two pieces of wood which I took from the door of the house where the crime took place. You will find on these two pieces the marks which without any doubt correspond with the hand of the woman Francisca Rojas.
"Dactiloscopia Comparada"
El nuevo sistema argentino) (1904).
Page 54.
We have the conviction that the finger schemes bear the necessary elements to establish the identity of people on any moment of their lives, in a definite and durable way. Moreover, thanks to these finger schemes, Justice reached great successes (2)
(2) In 1902, for instance, in Necochea, a woman called Francisca Rojas killed two of her children and put suspicion on an honest neighbour. As the local police didn’t have any success in this case, the chief of police sent commissioner inspector Eduardo M. Alvarez over to reinvestigate the case. At a moment of despair for not getting any new results, he found some – very faint - finger marks on a door. He asked the two pieces of the door on which the finger marks were found to be cut out and sent them to the judicial identification service where the whole truth was established, when proving that the mother of the victims was the real murderess.
"Proyecto de ley de registro general de identificacion" (1929 - with Luis Reyna Almandos) : Rojas case not mentionned.
(translations from the original Spanish texts by Gerlain Rodriguez Pajuelo and Johan Stimart)
So: Alvarez did the crime scene work and the first comparison. Vucetich verified.