Ten people were gunned down and 28 injured in the clash.
A relative of the main accused in the Sonbhadra clash was arrested from Varanasi, a senior police official said on Saturday.
Ten people were gunned down and 28 injured in the clash between supporters of Ubbah village headman Yagya Dutt and Gond tribals over a piece of land in Sonbhadra district's Ghorawal area on Wednesday.
Komal, a station superintendent in Bhadohi and a relative of Dutt was arrested Friday evening from Varanasi, Superintendent of Police (SP) Salman Taj Patil said Saturday.
On Friday, Chief Minister Yogi Adityanath had said 29 people, including Dutt, have been arrested and a sub-divisional magistrate and four policemen suspended.
"Komal a relative of Yagya Dutt, the main accused of the July 17 incident, has been arrested. Komal was arrested from Varanasi. He is the station superintendent of Bhadohi railway station," the SP said.
Mr Patil said that according to the members of the affected families, "Komal was present at the spot of the incident and also fired (on the tribals)".