He spent four years in prison on a reduced count of manslaughter.
He faces 5 to 15 years in prison if convicted on the manslaughter count.
He was charged with 16 counts of manslaughter in Baltimore.
The jury could not reach a verdict on the other two counts of manslaughter.
They'll probably end up at two counts of manslaughter if they can agree on the sentence.
The motorman, who left the scene, was charged with five counts of manslaughter.
He was convicted of two counts of manslaughter and died in prison.
Four decades later, Killen was brought to trial again and convicted last year on three counts of manslaughter.
The jury found him guilty of three counts of manslaughter on June 21, 2005.
The jury deadlocked, 8 to 4 for acquittal, on a second manslaughter count.