Scientific tests on Krishna, a key suspect in the Aarushi murder case, got underway at the Bowring Hospital in Bangalore on Thursday.

Krishnamurthy, joint director of the Central Bureau of Investigation said they obtained the permission to undertake the tests.

Forensic lab sources told rediff.com that Krishna would be subjected to brain-mapping first and if time permits they would also conduct the narco-analysis later in the day.

The results of both the tests will be corroborated along with the answers given by Krishna during the earlier interrogation.

It is also learnt that Krishna may be kept in Bangalore for a week. The CBI is taking no chances and want to take the accused back only once all the tests are conducted.

Legal experts say it is mandatory under law that permission is granted by a court of law before the tests are conducted. Instances where courts have granted permission for a second test are rare as there is a raging debate across the country regarding the authenticity of the test and whether it is required at all.

Krishna, a compounder in Aarushi's father Dr Rajesh Talwar's clinic Krishna was picked up the CBI in connection with the murder case in Noida.