Four persons including main accused Vipin Yadav, have already been arrested. The other main culprit identified as Rajesh is absconding.
The All India Kisan Sabha (AIKS) urged Singh to take up the issue with Rajasthan government to offer Rs one crore compensation to the victim Pehlu Khan's kin.
It also demanded the state to offer government job to Khan's relative and Rs 25 lakh compensation and free treatment to other victims of the April 1 incident.
Besides Mollah, CPI(M) MPs Jitendra Chaudhury, Sankar Prasad Datta and Mohammed Badaruddoza Khan and AIKS finance secretary P Krishnaprasad met Singh.
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Meanwhile, the AIKS has decided to collect fund from villages across the country to extend monetary help to Khan's family.
The AIKS has also asked its units to organise communal amity meetings in the memory of the deceased in villages before April 30.
Pehlu Khan and four others were attacked by the cow vigilantes in Alwar's Behror while they were on their way to Haryana after purchasing cattle in Rajasthan's Ramgarh.
55-year-old Khan succumbed to his injuries on April 3.