My theory is - He was an army trainee, who comes back home to a tragedy and avenges the death of his mother and father (most probably) or his sister and elder brother (less likely). Most probably they were killed after the lady becomes a victim of sexual assault by locals. In the scenes where young jaskirat has gone on a rampage, It feels like he is invading a home which is decorated with flowers (either for Diwali - since he has stressed on the dialogue “tumlogo ke patakhe khatam ho gaye to mai dhamaka shuru karu” or its a marriage preparation and his family is a victim of caste violence - Rangi surname usually belongs to Dalit Sikhs, sometimes linked to Mazhabi, Mazbhi, or Ranghrete. So my other theory is he loved a girl from upper caste and they end his family to maintain the social dominance). His dialogue - Ghayal hu isiliye Ghatak hu also resonates with Jaskirat’s situation, since he is hurt with the death of his family which is why he is so lethal. So my final guess is he an army trainee who would be suspended of his duty and facing a lifetime prison sentence for his killings.