Brazil has opened the trial of a man suspected of murdering 42 boys and castrating them.

During the first day of trial Monday, defendant Francisco das Chagas Rodrigues de Brito, 41, admitted that he murdered a 15-year old boy in 2003. 

The bicycle mechanic says he was sexually abused when he was a child and was acting in revenge.

Prosecutors say Chagas committed 42 murders but they have charged him with killing the 15-year-old, because it is the case they have the most evidence to support.

Chagas previously confessed to the other murders, but later recanted.

He could face up to 30 years in prison if found guilty.

Police believe he murdered 30 boys in Maranhao state and 12 in neighboring Para state between 1991 and 2003.

If found guilty of all the murders, Chagas would be Brazil's worst serial killer surpassing the so-called "Vampire of Niteroi," who was convicted of killing 14 people in the 1990s.

Some information for this report was provided by AFP and AP.