"Only after hanging will the right message go in the state," Fadnavis told the state Assembly.
"This is a very serious crime. DNA evidence is scientific evidence and will help in conviction. A five-member team, including forensic experts, will help bring the case to charge sheet level in next 4 to 6 days," he said, replying to a discussion on the issue in the Lower House.
Fadnavis said the state government will ask court to hang the guilty.
The brutal gangrape and murder of the girl had rocked both the houses of Maharashtra Legislature yesterday as its monsoon session got underway and a debate on the issue was held today in the Lower House.
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The crime had sparked protests across the state, with people taking to the streets demanding action against the accused, while Congress demanded the resignation of the CM on moral grounds.
"I appeal to people in the state to stop venting their ire over the issue," he said.
"It is difficult to believe that someone could indulge in an act which is worse than that of a dog," he said.
"All three accused have been arrested. Action will also be taken against the fourth accused," he said, adding that the CID will probe if Jitendra Shinde, an accused, had a role in an old murder case.
He said Pune Police Commissioner Rashmi Shukla will be directed to meet the victim's kin and talk to villagers.
"Guardian minister and senior police officials visited the village. I could not visit as I was away in Russia," Fadnavis said.
Over 90 per cent of crimes against women involve known persons, he noted.
The Kopardi rape has blackened the face of Maharashtra, Fadnavis said.
Earlier, former Deputy Chief Minister Ajit Pawar,
while participating in the debate, said the investigation should be such that those involved should be hanged in six months.
Leader of Opposition in Assembly Radhakrishna Vikhe Patil said action in Kopardi like cases should be on the similar lines as that of atrocity cases.
"Why is there no dedicated Home minister for the state?. Why does Fadnavis want to keep that portfolio with himself?," he said.
However, Shinde denied the charge.
BJP legislator Manisha Chaudhury blamed films like "Sairaat" for rise in crimes against women.
The girl was brutally raped and killed by three men at Kopardi in Ahmednagar last week.
The incident took place on July 13, when the teenage girl was returning after meeting her grandfather.
She was allegedly accosted by three men, who gangraped her before strangling her.
The victim, a student of class IX, had reportedly been mutilated, and local accounts suggest she was found with her hair pulled out, and hands and teeth broken.
Meanwhile, protesting over the incident, activists of a social organisation allegedly set on fire a bus near a village in Latur district today.
Several organisations today called for a bandh in Latur district to protest the incidentr.
This afternoon, around 4-5 supporters of Chhava Sangathana waylaid a State Transport bus going towards Kalamb from Latur city near Bhoi Samudraga village and asked the passengers to alight, police said.
"The moment the bus driver, conductor and passengers got down from the bus, these supporters torched the bus from inside in which all the seats were gutted," Sudhakar Bawakar, Assistant Police Inspector, MIDC police station Latur, said.