According to the police, R Gunasegaran, 31, had died from a drug abuse.
This was claimed by three witnesses who were said to be detained in the same lockup with Gunasegaran, she stated in her police report.
In view of this, Ganga Gowri is urging the authorities to perform a thorough and transparent investigation into the allegations.
She is also demanding that hospital authorities release the autopsy report if there is one, and for the police to initiate an inquest.
She was speaking at a press conference, organised by lawyer Harris Ibrahim and attended by six other lawyers.
"These (witnesses) are very afraid. They do not wish the authorities breathing down on them and shall remain anonymous.
"Should there be a transparent inquest, I have been given assurances that these people will surface," said Ganga Gowri's counsel M Visvanathan.
Visvanathan, said the witnesses alleged that Gunasegaran died within two to three hours of his arrest at about 7.30pm.
He added that the witnesses said that Gunasegaran was kicked in the chest, hit with a hose and a piece of wood.
However, Ganga Gowri had not examined the body for wounds, which is still at the Kuala Lumpur General Hospital mortuary.
Body still not claimed
She will not claim the body until a post-mortem and toxicology report is released.
Visvanathan said that although the standard practice by the authorities is to release the reports after two months, this had to be changed.
"It is insane to have the family claim the body and perform funeral rites and then wait for the post-mortem report, say for instance if the body had evidence of an assault whilst in detention," added Harris.
Former Bar Council Human Rights Committee chairperson Edmund Bon said there appears to be inconsistencies in the way the government deals with custodial deaths.
He said it was only with sufficient public pressure, where full blown investigations will be carried out, such as in the case of DAP political aide Teoh Beng Hock, who incidentally was found dead on the same day as Gunasegaran.
He urged the government to heed repeated request by NGOs and civil societies for the establishment of a Coroners Court as magistrates conducting inquest, were not sufficiently trained in this area.
Police chief promises action
Meanwhile, KL police chief Muhammad Sabtu Osman said that the police will investigate the matter thoroughly to find the truth.
"We cannot let this matter just like that. We will investigate thoroughly," he told reporters.
He added the police will have a look at the report lodged by the family.
"We will take action against any person found to have been involved in the detainee's death, even if it involves my personnel,"invovles my personnel," he added.