CBI sources said the takeover was according to rules and the agency has re-registered the FIR of the Goa Police which had said it was case of unnatural death.
When asked about the development, CBI Press Information Officer R K Gaur said the agency has taken over investigation in the case and the probe is on.
According to the rules, CBI takes over same FIR which was registered by local police but after investigation, its final report may add charges or discard allegations mentioned in the police report.
She was shifted to St Anthony's Hospital in Anjuna beach where she died on April 16, 2010 during treatment, it claimed.
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The autopsy had claimed that she had died because of 'cerebral pulmonary oedema' (accumulation of fluid in brain and lungs) with multiple injuries on her body but could not determine the causes of the medical condition, the sources said.
"The chemical analysis report indicates neither drugs nor
The local police has apparently botched up the probe with the viscera being sent to the laboratory 20 months after the incident whereas it should have been sent within six months of the autopsy.
Senior officials of Goa Police had admitted the botch-up in sending the viscera for examination saying it was sent to Regional Forensic Science Laboratory at Surat in November 2011 which yielded in inconclusive results.
The sources said role of a foreign national who was present at the site is also under scanner.
After the post-mortem at Goa Medical College and Hospital, forensic experts had reserved opinion on the cause of death, waiting for viscera analysis.
Denyse's body was sent to her native place, Derbyshire, after the autopsy here. Her sister Maureen had started a campaign suspecting foul play as there were multiple wounds.
She had got a second autopsy done in Britain which reportedly had ruled out presence of any trace of alcohol or drugs in the body.