Certain kinds of drugs can enable a person to go without sleep for a long time. These were also young men, possibly teenagers, so their stamina level would be high.
I hope they find out EXACTLY who hired and trained them, and the masterminds behind this atrocity neutralized quickly.
You were right about the terrorists using drugs:
“Sources said tests on Kamal’s blood and urine showed he was under the influence of drugs to help keep him alert during the long battles with Indian security forces.”