The pack belonged to a man upset by a dispute with the bank; police chose to treat the object as a threat, just in case.
"In today's world you can never be too careful," said Lt. Paul Ciesielski, Indianapolis Police Department spokesman.
The incident blocked two Downtown Indianapolis streets and closed an office building for 21/2 hours.
Kevin McDermott, 44, 100 block of East Ninth Street, was booked on a preliminary charge of terroristic mischief, a felony, and was being held Thursday at the Arrestee Processing Center. No bond was immediately set.
Police said McDermott had a dispute with Fifth Third Bank about a check and had previously complained at the bank branch at 251 N. Illinois St. in the Capital Center. McDermott returned to that branch just before noon Thursday, wandering around the bank and the Capital Center lobby.
After 11/2 hours, bank workers called police, who got to the bank around 1:15 p.m. Thursday. They found McDermott sitting in the bank lobby; his backpack was in a chair next to him.
McDermott was handcuffed and taken from the bank, while police called a bomb squad dog to check the backpack. When the dog sniffed the bag, the animal indicated something suspicious, police said.
That led police to call for the Marion County Emergency Management Agency, which sent Omega. The remote-controlled robot is designed to handle security and ordnance disposal. The Emergency Management Agency has a twin robot named Alpha.
"I was just pushing the buttons," said Steve Robertson, Omega's operator. "The whole purpose was that the human bomb technician doesn't have to be exposed."
Brought to the scene in a truck, Omega was directed inside the bank branch, where it X-rayed the pack. Those X-rays proved inconclusive, so the water cannon blasted open the backpack to reveal only clothes inside.
When all doubts about the backpack were removed, the office building was reopened. The first three floors of the Capital Center's north tower had been evacuated; workers on the remaining floors were told not to leave.
Outside, traffic was blocked on New York and Illinois streets until 4:15 p.m. Thursday.