New Delhi, Sep 10 (IANS): While convicting four people involved in the Dec 16, 2012 gang-rape, a district court Tuesday praised Delhi Police investigators for their prompt and professional action.

Additional Sessions Judge Yogesh Khanna, after announcing them guilty under several charges, including gang-rape, murder, unnatural offence, destruction of evidence and dacoity, praised Delhi Police officers for their hard work.

"Lastly, I feel it necessary to maintain the professional acumen with which the Delhi police investigated, especially ... use of scientific tools. I hope this would be replicated," Khanna said.

The four - Pawan Gupta, Mukesh, Akshay Thakur and Vinay Sharma - were found guilty by the court that decided to announce quantum of sentence Wednesday.

Dec 16, a 23-year-old trainee physiotherapist was gang-raped in a moving bus by six people, including a juvenile. Aug 31, the juvenile was remanded in a reform home for three years by a juvenile justice board.

The main accused, Ram Singh, was found hanging in his Tihar Jail cell March 11.