AURORA, Ill. | Federal investigators have collected more images showing that an Aurora radio tower's lights were on just before a medical helicopter crash that killed an Indiana pilot and three others.

John Brannen of the National Transportation Safety Board said Friday that still images from a security camera a few miles away from the crash site show the tower's upper and lower lights flashing before last week's crash.

Earlier this week, investigators recovered video from a train station parking lot.

With no sign that the helicopter had engine problems, a key question had been whether the tower's lights were on.

The Air Angels helicopter piloted by Del Waugh, 69, of Carmel, Ind., was transporting a 1-year-old patient when it clipped a guy wire and crashed, killing all four people aboard.