Four persons arrested in May this year in connection with the 1993 Mumbai serial blasts after being on the run for 29 years were "actively involved" in its criminal conspiracy, the Central Bureau of Investigation said in its supplementary charge sheet filed in a special court here.

On March 12, 1993, a total of 257 persons were killed and more than 1,400 injured after 12 blasts took place in the country's financial capital.