Terming as 'a terrible thing,' the arrest of two girls in Mumbai last month under 66A of the IT Act for their Facebook posts,former Chief Justice of India M N Venkatachaliah today said police should know on what grounds they were making such arrests.

"It is a terrible thing to happen. Police has the power to arrest, but they should know on which grounds the arrests are made," he said to a question by a reporter tonight on the post, just after the death of Shiv Sena supremo Bal Thackeray.

On November 18, Shaheen Dhada and Renu were arrested at Thane over their Facebook post,questioning the shutdown in the city for Thackeray's funeral that day.It also led to an attack on the clinic of an uncle of one of them by Sena activists.

The girls were sent to 14-day judicial custody by a court before which they were produced but were granted bail within hours after they furnished personal bonds.

Asked for his views on the death sentence, the former CJI, here to release a book,said though there are exceptions in some cases, there should be a national debate on whether there should be capital punishment.

To another question on encounter deaths,Venkatachaliah, a former chairman of National Human Rights Commission, said in rare cases, a police official can open fire in self defence. "However, killing a person after tying him up and immobilising him should be questioned," he said.

He said the present situation India was like in pre revolution days Russia, China and France,as 30 per cent of the population do not have faith in social justice and justice of governance.