The cause of the manhole explosion that killed a Con Ed worker is still being investigated Friday, a day after the accident.

George Dillman was killed Thursday afternoon while he was working about 10 feet underground on a 120 volt cable. Witnesses say his partner, Craig Penney, could do nothing to help Dillman as flames began to shoot up.

Dillman's colleagues honored him by scrawling messages on a burnt Con Ed hard hat, which hangs above a small memorial at Euclid and Sutter avenues, the site of the explosion.

A spokesman for Con Ed says the utility is cooperating fully with a joint federal-state investigation into the blast.