This is not an old-up – 'elderly' bank thief may be young crook in mask

The Geezer Bandit during a robbery on a bank in California in April last year (AP)

Detectives hunting a prolific armed bank robber dubbed the "Geezer Bandit" have searched a costume store in central California where they believe he bought the face mask that makes him appear elderly.

The crook, who has struck 16 times in two years across the region, is now believed to have carried out the heists while wearing a brand of silicone mask known as "The Elder".

He also appears to wear gloves that give his hands a wrinkled appearance.

Detectives ave suspected since last year that the audacious crook was in fact a young man.

However their theory was not confirmed until 2 December, when they reviewed security camera footage of his most recent robbery, in the coastal town of San Luis Obispo.

The crime went awry when a device planted in the carrier bag of cash the Geezer Bandit was carrying out of the bank exploded, spraying red dye over him.

In an apparent panic, he sprinted across the car park into his getaway vehicle.

FBI investigators said in a statement that his speed suggested he was relatively young and fit. They recently served a search warrant on a local costume store, demanding a list of all customers who bought The Elder.

They are also analysing a diary he apparently dropped at the scene.