MIDDLETOWN, Conn. (AP) — Federal and local authorities are in court arguing over custody of a key piece of evidence that could shed light on the cause of a Connecticut power plant explosion that killed six workers.

Officials with the U.S. Chemical Safety and Hazard Investigation Board are asking a state judge in Middletown to order local police to turn over a gas-detection meter from the plant so the board can examine it. Local police say they're worried that giving the unit to other agencies could jeopardize their investigation.

Attorneys liken the meter to a crashed airliner's "black box."

The hearing began Tuesday morning and was to continue later in the day.

Some workers have said they noticed an unusually strong gas smell just before the Feb. 7 blast in Middletown.