NEW DELHI — A member of a Hindu vigilante group organized to protect cows was among five men arrested on Saturday in connection with the murder of two Muslim cattle traders, who were beaten and then hanged from a tree, the police said.

The two victims were leading oxen to be sold at an animal fair before dawn on Friday when they were spotted by Awadhesh Sahu, a Hindu man, said Purushottam Singh, a police officer in Latehar, a district in the eastern India state of Jharkhand.

Mr. Sahu said he believed that the two were leading the animals to slaughter and summoned seven friends to intercept them on the highway. The group surrounded the cattle traders, Mohammad Majloom Ansari, 32, and Mohammad Ibrahim Ansari, 13, took them into the forest and beat them, in an assault that lasted about 90 minutes, Mr. Singh said.

The police were cautious about identifying a motive in the killings, noting that members of the same vigilante group confessed to extorting money from Muslim cattle traders on at least three earlier occasions. Mr. Singh also noted that one of the assailants had a personal grudge against the family of at least one of the victims.