"We were beaten as if we were footballs," says Kamal's younger brother Nirmal, who was also interrogated but allowed to go after his brother's death. "They said to me - either confess or we will kill your brother," he claims.
On Thursday morning, Kamal was found hanging in lock-up.
All 15 policemen of the outpost have been suspended and one has been accused of murder. Some of the policemen are missing.
News of the death brought a large group of protesters to the police post. The mob clashed with the police and threw stones at them.
Valmiki's family alleges that he died after the severe beating. Kamal and Nirmal were allegedly taken away by a constable named Janardhan, who now faces a murder case.
"I only want my other sons to be safe. We are poor. How can we take on the might of the police?" wept Kamal's father Kishan Valmiki.
In one of their many questionable moves, the policemen sent the body for a post-mortem under a different name - Raju Mistry.
The police claim the name change was a mistake, not deliberate. But a search is also on for the real Raju Mistry, who is missing.
"A custody death is absolutely unacceptable," Uttar Pradesh police chief Javed Ahmed told NDTV.
Among the questions begging investigation are how a man committed suicide in the presence of so many cops and how he found rope to hang himself.
The Akhilesh Yadav-led Samajwadi Party government in Uttar Pradesh is confronting opposition anger over the state of law and order as it campaigns for re-election in polls next year.
Dalits form nearly 21 per cent of the state's voters. Former chief minister Mayawati, a Dalit powerhouse, has pivoted her campaign on alleged atrocities against the underprivileged.
"A Dalit has died in custody. Only suspending policemen is not enough," she told reporters.
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