COLOMBO, Sri Lanka — The suicide bombs were packed with ball bearings, iron nails and the explosive TATP, all hallmarks of the way the Islamic State likes to commit mass murder.

One of the bombers had traveled to Syria. Another trained in Turkey. One man arrested hours after the attacks had commuted between Sri Lanka and Syria, leading investigators to identify him as a possible middleman between the Islamic State and Sri Lankan militants.

As Sri Lankan investigators reveal key details from the suicide blasts that killed more than 250 people in churches and hotels across the island on Easter Sunday, more evidence points to a role by the Islamic State in inspiring — and perhaps directing — the slaughter.

Even as the Islamic State has been routed from territories in Iraq and Syria where its black flag once flew with impunity, the Sri Lanka attacks show the group is still capable of orchestrating carnage through loyalists in far-flung countries.