Harare - A human rights group in Zimbabwe on Tuesday condemned a "grave and wanton attack" by state security agents on the brother of missing activist Itai Dzamara, who mounted a silent protest at Independence Day celebrations in Harare.Author and academic Patson Dzamara was "allegedly coerced to drink lots of water, forced to kneel in an uncomfortable position, assaulted with booted feet and fists, and later interrogated at the Central Intelligence Organisation section of the Harare Central Police Station".This happened after he held up a placard asking where his brother was, during an event at the National Sports Stadium on Monday, the Zimbabwe Human Rights Association (Zimrights) said.According to Occupy Africa Unity Square, the organisation that was supporting efforts to find Itai Dzamara, Patson was holding his placard outside the VIP tent at the stadium, near where President Robert Mugabe addressed the crowds. @ZimMediaReview posted a photo of Patson Dzamara in a private hospital on Monday night after he was released. "Assaulted by security officials for protesting the abduction of his brother," tweeted the press watchdog. He was bruised and had a sprained ankle.Itai Dzamara was abducted from a barber shop in a Harare township on March 9, 2015.The opposition Movement for Democratic Change and government critics believed Mugabe's government was behind his abduction, and there were fears he was dead.Zimrights said the attack on Patson Dzamara was "gruesome and sadistic". The fact it had happened on Independence Day was "a sad reflection of the road Zimbabwe has unfortunately chosen to pursue".