MILLERSVILLE — Federal investigators say a poorly installed natural gas connection is likely to blame for a gas explosion that killed a utility worker and destroyed two Pennsylvania homes in July 2017.

The National Transportation Safety Board said Thursday the faulty connection let gas seep into the house in Millersville.

The blast also injured three other people and caused significant damage to six nearby houses, including one that was later condemned.

Authorities say a locking sleeve used to connect the “tapping tee” to the gas main was not attached to the main.

The unattached locking sleeve put stress on four nylon bolts, and two of those bolts fractured.

A UGI Utilities employee was killed in the explosion.