HOUSTON -

A man on trial after surveillance cameras captured him robbing local jewelry stores, melting down gold and selling it for cash has been convicted.

Kelvin O'Brien is accused of one of the biggest jewelry heists. On Wednesday afternoon he represented himself in closing arguments of his own trial.

O'Brien and a few other men are accused of pulling off a professional-style burglary at the southwest Houston jewelry store, Karat 22, on Hillcroft back in 2011.

Prosecutors say O'Brien and others broke into the roof, managed to cut through a vault inside and get away with more than $6 million in jewelry.

"The people that money, that gold jewelry was stolen from... it's a big deal to them.  It's a big deal to the Patel family that was inside watching today because they lost millions of dollars and they lost jewelry that's been in the family for generations and can't be replaced," said prosecutor John Brewer.

After the burglary, prosecutors say those involved, including O'Brien, who ended up firing his attorney and representing himself, melted the gold down then sold it for cash.

O'Brien is accused of using the cash to buy a Mercedez, a Range Rover, a boat and a home.

It only took the jury about 30 minutes to reach the guilty verdict Wednesday afternoon.