Texas has executed a self-described "non-caring monster" for killing his two stepchildren. They were among five relatives he took responsibility for killing.

Thirty-four-year-old Terry Lee Hankins said he was "sorry for what I've done" from the death chamber gurney before he was executed. He was pronounced dead at 6:19 p.m. Tuesday.

Hankins surrendered in 2001 after a five-hour standoff with police who wanted him for gunning down his estranged wife and her two children. Hankins then told officers he'd killed his father and half-sister almost a year earlier.

Hankins was tried only for the children's deaths.

His was the 16th execution this year in Texas, the nation's most active death penalty state.