Three suspected attackers have been detained, along with two policemen accused of dereliction of duty and criminal conspiracy.
The girls, who belonged to a low caste, were found hanged from a tree in Uttar Pradesh state earlier in the week.
Alleged police inaction has sparked outrage.
The father of one victim said he was ridiculed by police when he sought help in finding his missing daughter.
The government has pledged to set up a fast-track court to deal with the case.
Meanwhile, reports have emerged that two more gang rapes of minors occurred in Uttar Pradesh, in northern India, this week.
The chief minister of Uttar Pradesh mocked female journalists when asked about the rising number of rape cases at a news briefing.
“You are safe, why are you bothered?” Akhilesh Yadav said.
“No other state has the kind of police control room we have here. If there is any incident, we will take action.”
Police say they are now calling off their search for suspects over the attack.
Among those arrested are two officers, who have also been sacked over claims they refused to help look for the girls.
Senior police official Atul Saxena earlier announced there would be a “thorough investigation” into the allegations of caste discrimination by police.
Divisions between India’s castes run deep, and violence is often used by upper castes to instill fear in lower castes, correspondents say.
Although both the victim and the accused in the latest case belonged to a group known as “Other Backward Classes”, the victims were lower in that hierarchy.
The girls, two cousins aged 14 and 16, went missing in Badaun district on Tuesday night. They had apparently gone out to relieve themselves as they had no toilet at home.
Their bodies were discovered the following day. A post-mortem examination confirmed multiple assaults and death due to hanging.
The victims’ families say it took police more than 12 hours to respond to reports they were missing.
Campaigners have highlighted the lack of sanitation in rural areas as being a risk to women’s security as well as their health, as they are often attacked when having to go out to use the toilet, particularly at night.
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