Story highlights Suspect's lawyer: "There was no reason for him to commit suicide"

The parents of Ram Singh say he was murdered

He was accused of raping and fatally beating a woman in a gang assault on a New Delhi bus

The attack prompted angry protests over the country's treatment of women

One of the men accused of gang raping and fatally beating a woman on a New Delhi bus was found dead in his jail cell Monday.

Police say Ram Singh hanged himself. But his lawyer and parents claim he was murdered.

"There was no reason for him to commit suicide. There is some foul play," Singh's attorney V.K. Anand said.

Singh was housed in New Delhi's Tihar Prison. Last year, the prison recorded 18 deaths, including two suicides, according to CNN affiliate CNN-IBN.

"Ram Singh did not kill himself. He was murdered," Singh's father, Mangi Lai, told the affiliate.

Photos: Photos: India rape protest Photos: Photos: India rape protest India rape protests – An Indian activist gets his head shaven in protest against the Dehli gang-rape in New Delhi on Friday, January 4. A gang of men is accused of repeatedly raping a 23-year-old student on a moving bus in New Delhi. Police formally charged the five suspects with rape, kidnapping and murder after the woman died. Hide Caption 1 of 29 Photos: Photos: India rape protest India rape protests – Indian lawyers shout during a protest at the entrance to Saket District Court in New Delhi on Thursday, January 3. Hide Caption 2 of 29 Photos: Photos: India rape protest India rape protests – About 600 guitarists play John Lennon's "Imagine" in a tribute to the rape victim in Darjeeling on January 3. Hide Caption 3 of 29 Photos: Photos: India rape protest India rape protests – Indian women take part in the Women's Dignity March in New Delhi on Wednesday, January 2. Several hundred people participated in the solidarity march organized by the government, which ended at Rajghat, the memorial for Mohandas Gandhi. Hide Caption 4 of 29 Photos: Photos: India rape protest India rape protests – Delhi Chief Minister Sheila Dikshit, center, participates in a group prayer during the Women's Dignity March on January 2. Hide Caption 5 of 29 Photos: Photos: India rape protest India rape protests – Indian demonstrators perform a prayer ritual in memory of a gang-rape victim in New Delhi on Monday, December 31. The family of the victim said they would not rest until her killers are hanged as they spoke of their own pain and trauma over a crime that has united the country in grief. Hide Caption 6 of 29 Photos: Photos: India rape protest India rape protests – A Sri Lankan opposition United National Party activist places her signature on a banner in memory of the Indian gang-rape victim in Colombo on December 31. Hide Caption 7 of 29 Photos: Photos: India rape protest India rape protests – Indian protesters hold candles during a rally in New Delhi on Sunday, December 30, following the cremation of the gang-rape victim. Hide Caption 8 of 29 Photos: Photos: India rape protest India rape protests – Indian protesters walk with police officials during a rally in New Delhi on Sunday, December 30, following the cremation of a gang-rape victim in the Indian capital. The 23-year-old student died Saturday and was cremated at a private ceremony, hours after her body was flown home from Singapore. She had been gang-raped and severely beaten on December 16, triggering an outpouring of grief and anger across India. Hide Caption 9 of 29 Photos: Photos: India rape protest India rape protests – Indian protesters sit by lit candles and hold placards in New Delhi on December 30 during a protest against the gang rape. Hide Caption 10 of 29 Photos: Photos: India rape protest India rape protests – Indian residents pray during a gathering in New Delhi on December 30. Hide Caption 11 of 29 Photos: Photos: India rape protest India rape protests – Protesters hold candles during a vigil in New Delhi on Saturday, December 29, after the death of a gang-rape victim. Authorities erected security barriers throughout New Delhi's key government district after two days of street battles following a woman's gang rape on a bus on December 16. Indian Prime Minister Manmohan Singh has appealed for calm and pledged safety for women and children. Hide Caption 12 of 29 Photos: Photos: India rape protest India rape protests – Indian residents hold lighted candles during a rally in Amritsar on December 29. Hide Caption 13 of 29 Photos: Photos: India rape protest India rape protests – Students in New Delhi on Thursday, December 27, protest a recent brutal gang rape in the city. Hide Caption 14 of 29 Photos: Photos: India rape protest India rape protests – Demonstrators shout slogans and wave placards as they move toward India Gate in New Delhi on December 27. Hide Caption 15 of 29 Photos: Photos: India rape protest India rape protests – Riot police keep watch along a sealed-off road near the India Gate monument on Monday, December 24, in New Delhi after weekend clashes between protesters and police. Hide Caption 16 of 29 Photos: Photos: India rape protest India rape protests – Police fire tear gas on Sunday, December 23, during a protest calling for better safety for women following last week's rape. Thousands of protesters defied a ban on demonstrations in New Delhi on Sunday, venting their anger about the incident. Hide Caption 17 of 29 Photos: Photos: India rape protest India rape protests – Police attempt to disperse protesters on December 23. For a second day, demonstrators were blasted with water cannons in the Indian capital. While some dispersed, others huddled tightly in a circle to brave high-pressure streams in the cold weather. Hide Caption 18 of 29 Photos: Photos: India rape protest India rape protests – Demonstrators turn a car over on December 23. Hide Caption 19 of 29 Photos: Photos: India rape protest India rape protests – Students chant anti-police slogans during a protest against the Indian government's reaction to recent rape incidents in India, on Saturday, December 22, in New Delhi, India. The demonstration was prompted by wide public outrage over what police said was the gang-rape and beating of a 23-year-old woman on a moving bus in the capital last Sunday. Hide Caption 20 of 29 Photos: Photos: India rape protest India rape protests – Demonstrators react from tear gas fired by police on December 22. New Delhi alone reported 572 rapes last year and more than 600 in 2012. Hide Caption 21 of 29 Photos: Photos: India rape protest India rape protests – Police arrest a demonstrator during a protest on December 22. Sunday's attack sparked furious protests across India, where official data show that rape cases have jumped almost 875% over the past 40 years -- from 2,487 in 1971 to 24,206 in 2011. Hide Caption 22 of 29 Photos: Photos: India rape protest India rape protests – Police unleash water cannon and fire tear gas towards demonstrators on December 22. Hide Caption 23 of 29 Photos: Photos: India rape protest India rape protests – Demonstrators react as police fire tear gas on December 22. Hide Caption 24 of 29 Photos: Photos: India rape protest India rape protests – Indian demonstrators march towards India Gate during the protest on December 22. Hide Caption 25 of 29 Photos: Photos: India rape protest India rape protests – Indian demonstrators carry an injured man from the scene on December 22. Hide Caption 26 of 29 Photos: Photos: India rape protest India rape protests – Police spray water and fire tear gas towards demonstrators on December 22. Hide Caption 27 of 29 Photos: Photos: India rape protest India rape protests – Demonstrators push against a police barricade on December 22. Hide Caption 28 of 29 Photos: Photos: India rape protest India rape protests – Students chant anti-police slogans on December 22. Hide Caption 29 of 29

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New Delhi's Chief Minister Sheila Dikshit said she has ordered an inquiry.

Authorties say Singh was the driver of the bus aboard which several men brutally raped a 23-year-old woman on December 16.

The gang rape, and the woman's subsequent death from injuries, prompted angry protests over the country's treatment of women and handling of sexual attacks.

Police charged Singh and four other men with murder, rape and kidnapping.

Their trial began in February. If convicted, the men could face the death penalty.

A sixth suspect is 17 and will be tried separately in juvenile court.

The December rape gripped India and led to calls for stricter laws on sexual assault and changes in cultural attitudes toward women.

Most Indian women have stories of sexual harassment and abuse on public transportation or on the streets, according to the Indian Council on Global Relations.