New Delhi: The mother of the 23-year-old paramedic student, who was brutally gang-raped and murdered in 2012, Tuesday said she approached the Delhi Commission for Women to look into the "delay" in execution of the convicts.

The DCW issued a notice on Monday to Tihar Jail authorities over "delay" in execution of convicts in the December 15, 2012 Nirbhaya rape and murder case.

Urging the authorities to hang the convicts "as soon as possible", Nirbhaya's mother Asha Devi said she wants justice for her daughter and it would not be served till her murderers are executed.

She said she again approached the DCW in July to look into the delay in execution of convicts.

Devi had complained to the DCW last year too, asking why the criminals have not been hanged as per the Supreme Court order.

In May last year, the Supreme Court upheld the death sentence to four men convicted of the savage rape and murder of the 23-year-old paramedic student, terming it as an attack "most brutal, barbaric and diabolical".

In July, the apex court dismissed review pleas filed by three of the convicts while the fourth convict did not seek a review.

Issuing the notice to Tihar Jail authorities, DCW Chairperson Swati Maliwal demanded an explanation over the "delay" in execution of these convicts.

She said that they "should be executed at the earliest in order to create a strong deterrence in the society".

Six men had assaulted the woman, who was later known as "Nirbhaya" (the fearless), and a male friend in a moving bus as it drove through the streets of New Delhi.

She was thrown out of the bus - so grievously injured that her insides were spilling out - along with her male friend near the airport. A fortnight later, on December 29, 2012, she succumbed in a hospital in Singapore.