The girl, who was working at Siddhi Engineering in Mahad town, was found dead under mysterious circumstances on April 26.
Her family members have alleged the she was murdered by the owner of the firm after she came to know about their "anti-social dealings".
Addressing a press conference here, the victim's sister alleged that police are trying to protect the accused.
"It has been over a month since the incident took place, but the police are yet to find the murder weapon or victim's mobile phone. I feel that enquiry officer is also involved in the planning of murder," she claimed.
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"Thus, I demand that the case should be handed over to to CBI or Special Investigation Team," she said.
She said she had written a letter to Maharashtra Governor, state Home Minister besides other officers, seeking their intervention into the matter.
She claimed in the letter that the FIR was registered 10 days after her sister's murder and that too after the intervention of Union Home Ministry.
Union Minister of State for Home Kiren Rijiju recently said he was in constant touch with the Maharashtra government, particularly the DGP and SP of Raigad district, for the investigation into the murder case.
She also claimed that there were indications that the victim was forced to have sexual relationship with the accused.
Unfortunately, the FIR has neither included offence under section 376 (punishment for rape) or offence under NDPS Act 1989, she alleged.
When contacted, Raigad SP Suvez Haque told PTI that accused has been booked under relevant sections of IPC.
"We have sent the sample (viscera) to JJ Hospital for examination by best forensic experts and are awaiting report," he said, adding that entire scene of crime has been videographed.