How one becomes a Ghost – Garuda Purana

Those who meet with foul death such as committing suicide by hanging from a tree, by poison or weapon, those who die of cholera, those who are burnt to death alive, those who die of foul and loathsome diseases or at the hands of robbers.

Those who are not cremated duly after death, those who do not follow sacred rites and conduct, those who do not perform Vrsotsarga and monthly pinda rites, those who allow sudras to bring sacrificial grass, twigs and other articles of homa.

Those who fall from mountains and die, those who die when walls collapse.

Those who are defiled by women in their menses, those who die in the firmament and those who are forgetful of Lord Vishnu, those who continue to associate with persons defiled due to births or death, those who die of dog-biting or meet with death in a foul manner, become ghosts and roam over the earth.

One who discards one’s mother, sister, wife, daughter or daughter-in-law without seeing any fault in them, obtains ghosthood surely.

One who deceives his own brother, kills a Brahmana or a cow, drinks liquor, defiles the preceptor’s bed, steals gold and silk garment, becomes ghosts.

One who usurps a deposit, deceives a friend, enjoys other man’s wife, kills other’s faith, is cruel, definitely becomes a ghost.

One who discards the family customs, takes to other customs, is without knowledge and good character, definitely becomes a ghost.

- Garuda Purana