Miss Pathak was a journalist working in Delhi
Police in India are questioning the father and brother of a Delhi-based journalist found dead last week in a suspected "honour killing" case.
Nirupama Pathak was found dead in her parents' home in Jharkhand state. An autopsy revealed that she was pregnant.
She was reportedly in a relationship with a man from a different caste.
On Monday Miss Pathak's mother was arrested in connection with her murder. Her family deny all the allegations and say she committed suicide.
Miss Pathak's family reported her death last Thursday. They said she was found hanging from the ceiling fan in her room and produced two suicide notes.
But an autopsy report showed the death was "a clear case of murder... caused by asphyxia as a result of smothering," the AFP news agency quoted senior Jharkhand police officer MS Bhatia as saying.
The autopsy also showed that Pathak was pregnant, fuelling suspicions that this was a case of honour killing, police said.
Miss Pathak, 22, was a high-caste Hindu Brahmin living in Delhi and reportedly in a relationship with another journalist, Priyabhanshu Ranjan, who was from a lower caste.
Police say that her parents had opposed the idea of their daughter "marrying someone from outside their caste".
Correspondents say that honour killings in the villages of northern India have long been reported.
But if Miss Pathak's case is found to be an instance of honour killing, it would be rare given her education and her urban background.