Danesh Puri and Nemi Puri were arrested and efforts were on to arrest other accused, Superintendent of Police Jitendra Singh said.
Besides the duo, some other accused were also named in the FIR filed by the youth's brother Anand Pandey, the SP said.
JMM MLA and party's Giridih candidate Jagannath Mahto and his brother were among the names in the FIR, the police officer said.
The 22-year-old youth, Santosh Pandey, was beaten to death at the "people's court" yesterday, convened by a group of villagers at Narah village under Nawadih police station of the district.
The police were investigating allegations that the "jan adalat" was convened after Pandey allegedly had been in love with a girl.