Four masked gunmen who knew their victims by nickname overpowered a janitor and bank manager and drove off with $3.3 million, apparently the largest cash haul from a bank heist in the nation's history.

"These guys did their homework.These guys are pros," said police spokesman Mike Walsh after the robbery of a First National Bank of Arizona branch by the two gunmen in Halloween masks and two with stocking hoods.

Chuck Hemann, First National spokesman in Phoenix, said that an audit revealed that $3.3 million was taken. Bank officials at first declined comment on the amount taken, although sources close to the investigation had estimated $2.5 million was involved.

Authorities said janitor Charles Virgil was sitting in his pickup truck in the parking lot before 7 a.m. waiting for the manager to arrive when a white van painted to look like a telephone company truck pulled up beside him.

According to a copyrighted report in the Tucson Citizen, Virgil said two masked men jumped into his truck, one on each side, and grabbed him. He said he kicked one in the chest before they each put a handgun to his temple.

"The next thing I know these two guys snatched me out of my truck still pointing the guns at my head and threw me into their van," he said. He was tied and gagged, he added.

He said one gunman kept calling him Charlie, and they referred to the bank manager, John H. (Bud) Grainger Jr., as "old bald-headed Bud." He said the robbers threatened to kill them and their wives unless Virgil and Grainger cooperated.

"If this doesn't go down right . . . you'll be the first one to be killed," he said one robber told him.

He said when Grainger arrived about 7:20 a.m. and turned off an outside alarm, the van sped up to the door and a gunman jumped out.

He said three of the gunmen forced the hostages inside the bank and made Grainger open a vault reportedly used to store cash receipts from the other 27 First National branches in Tucson. The fourth stayed in the van.

Virgil said the men stuffed money into a long black laundry bag, three knit fisherman-type bags, a travel bag and several bank sacks in less than 20 minutes.

They loaded the van and then fled, leaving Virgil and Grainger unharmed. No shots were fired, authorities said.

The van later was found abandoned with the Halloween masks inside, authorities said.