Juhani Aataminpoika was born Johan Adamsson on July 31, 1826, in Vesivehmaa, Finland. 

Juhani Aataminpoika began his series of murders in October 1849 after escaping from prison during transport to a court hearing. He first killed the master and mistress of the Helisevä croft in Lammi with a man named Kustaa Kratula. After that, he returned to his home in Heinola and killed his father, mother, and their two children.

Aataminpoika continued his violent spree by killing a man to obtain a job certificate for work at a canal site. He traveled to the Saimaa Canal, where he killed more people along the way. Once he reached the canal worksite, he did not stay long and killed a sailor to acquire his necessary papers.

At the beginning of November, Juhani returned to Lammi and joined his friend Antti Suikko. Together, they went to the Tyry croft in Hattelmala, where they vandalized the house and attacked the tenants. The elderly mistress of the house later died from her injuries, while the others survived the assault.

His series of murders came to an end when he was captured on November 20, 1849, in Palsa, near the border between Lammi and Padasjoki. After a trial, the Vyborg Court of Appeal sentenced him to death, but the Emperor commuted his sentence to 40 lashes and life imprisonment. He was transferred to Suomenlinna in January 1853, where he remained chained to a wall until his death in 1854.