It all began shortly after 9:30 a.m. at the M&T Bank branch at 3530 Philadelphia Pike.
Police say two suspects robbed the bank and fled toward Manor Avenue.
However, a satchel was left behind and there were concerns about what might be inside the bag.
Police immediately evacuated the bank and the surrounding area.
Authorities shut down Philadelphia Pike between Darley Road and Governor Printz Boulevard.
A bomb disposal robot was sent into the building around 11:30 a.m. and officers followed a short time later.
The robot was equipped with sensors for explosive materials and didn't detect any.
However, when a heavily armored member of the bomb squad went in, he smelled a suspicious odor coming from the object.
They then had to bring in a state hazmat team to investigate the odor.
Then authorities had to waiit for a specialized piece of equipment to be flown in from Dover by the State Police.
Nearby Archmere Academy High School was placed lockdown.
"We understand it's a very large disruption, but, unfortunately, because we don't know what it is in the bag, we have to take these precautions to make sure everyone is safe," Cpl. John Day of the Delaware State Police said.
The bag was cleared of anything hazardous and the incident was cleared shortly before 2:00 p.m.
The lockdown was then lifted.
The long investigation brought commerce to a standstill in the area.
This supermarket and other shops in the Claymont Shopping Center were shut down as employees gathered in parking lots waiting for the all clear.
Eventually investigators returned from the bank with a sealed bucket.
Inside the bucket were the items left behind by the bank robbers: a galvanized bucket with a hair product tube inside and water mixed with ammonia.
It appears to have been left to keep police occupied as the robbers fled.
"There's a possibility this is a decoy device meant to divert resources from the robbery investigation itself," Day said.
Authorities do not have a good description of the suspects as they were wearing masks.
Police are continuing their investigation.