New Delhi (CNN) One of six men convicted of brutally beating and raping a student on a bus in New Delhi in 2012 is asking the country's judiciary to spare him from the death penalty.

His argument? Air pollution is already killing him.

Akshay Thakur was one of four men sentenced to hang for gang-raping Nirbhaya, a 23-year-old woman, who died two weeks later as a result of her injuries.

A fifth suspect was released from prison because he was a minor at the time of the crime, and police said a sixth killed himself in prison.

Thakur's lawyer filed a review petition in the Indian Supreme Court Monday, just days before the seventh anniversary of the crime on December 16. Local media has speculated the men could be executed on the anniversary, especially considering the country has seen a string of similar shocking rape cases make international news in recent days.

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has some of the world's most toxic air. Earlier this year, seven Indian cities made Indiahas some of the world's most toxic air. Earlier this year, seven Indian cities made the list of the world's top 10 locations for air pollution.

However, it's unlikely Thakur's plea for leniency will work, according to criminal defense lawyer and legal expert Satish Maneshinde.

"He cannot avoid death penalty on these grounds," Maneshinde said.

Nirbhaya's mother, Asha Devi, told CNN in an interview that she is tired of waiting for her daughter's killers to be hanged.

"I cannot express how painful it is, in these seven years how much we have struggled, on a mental level the amount of torture that I have dealt with," Devi said of her wait for justice.

"We are sitting here with the hope that they will be hanged, but even after all that has happened they have not been punished," she said. "Until they are punished for their crimes, until the rapists are hanged, this will not stop."

The particularly savage descriptions of the 2012 gang rape elicited international outrage and scrutiny into how women are treated in the world's second-most populated country. Domestically, it prompted renewed scrutiny into how sexual violence cases are handled.

India passed new legislation in the case's aftermath, increasing punishments for sex crimes

Devi said she has been able to stay strong because she draws strength from her daughter's struggle.

"I have seen her dying, and I have seen her desperate for a single drop of water," she said. "There is no God for me, there is no one who gives me that power, but it is that pain that gives me that power."

'Like a gas chamber'

Singh's lawyer claimed in the petition that the air quality in New Delhi is "like a gas chamber" and the city's water is "full of poison."

"Life is going short to short, then why the death penalty?" the petition read.

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The prison where Thakur is held is located in Mayapurim, a particularly polluted area in west New Delhi, with many factories just kilometers away from the facility.

New Delhi has in the past been ranked the most polluted city in the world. Last month residents choked on record-breaking levels of smog more than three times the "hazardous" level on the global air quality index (AQI) and more than 20 times what the World Health Organization (WHO) considers "safe."

Maneshinde said that while most, if not all, convicted death row inmates attempt "delay tactics to frustrate the legal system," blaming pollution was unprecedented.

"This kind of plea has never been filed by an accused (criminal) before," he said.

Thankur's lawyer, A.P. Singh, denied that his client was using a delay tactic.

"He's a poor man. His parents are old and helpless. Pollution is anyway harming lives and killing people slowly," Singh said. "Give him a life term sentence, not the death penalty."