Scarlett was found dead with bruises on her body at Anjuna beach in Goa on February 18, 2008.
Two locals, Samson D'Souza and Placido Carvalho, were accused of leaving her to die after drugging and sexually abusing her.
The Goa Children's Court had acquitted both last year.
On appeal, the high court convicted D'Souza under IPC sections 328 (for administrating drugs), 354 (outraging woman's modesty), 304 (culpable homicide not amounting murder), and 201 (causing disappearance of evidence) and for child abuse under section 8(2) of the Goa Children's Act.
The arguments on quantum of sentence would be heard on July 19.
The high court, however, upheld the acquittal of Placido Carvalho.
The case, initially investigated by Goa Police, was handed over to the CBI by the state government after Scarlett's mother, Fiona Mackeown, raised doubts about the investigations.
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