They ran outside to a waiting car driven by Nathaniel Greenlee, 21, of Bear, Delaware; and containing passenger Donovan Jackson, 20, of Wilmington, Delaware, authorities said.
Plummer was a security guard who had been fired two weeks earlier, though investigators declined to say why. It was not immediately clear whether any of the suspects had hired lawyers.
At a news conference Thursday in Atlantic City, authorities said the suspects, particularly Plummer, appeared to know exactly what they were doing.
"It seems they had intimate knowledge of what would take place," said New Jersey State Police Capt. Christopher Leone. "They pulled up to a door on a side street not frequently used, and they had detailed knowledge where to look for the money."
Plummer and Evans were in and out of the casino within four minutes, Leone said.
But within hours, detectives came up with the name of at least one of the suspects, aided by a Caesars security guard who recognized one of them, Leone added. The two suspects who grabbed the cash inside the casino were each wearing masks.
All told, authorities have recovered about $150,000 of the stolen cash or merchandise purchased with it, including $50,000 worth of marijuana that was apparently intended for re-sale, high-end jewelry, sneakers and clothing.
Detectives arrested Plummer at his home the day after the heist, along with two 19-year-olds from Pleasantville: Monique Kelly and Dwayne Morgan. Authorities seized $43,000 in stolen cash; .38-caliber rounds and articles of clothing worn by the suspects during the commission of the crime.
On July 23, Evans and Lance Rogers, 20, of Atlantic City, were arrested at their homes. According to detectives, Rogers received stolen currency from Plummer. Investigators said they obtained a search warrant for Evans' residence and seized more stolen cash and various items connecting him to the robbery.
On August 6, state police from New Jersey and Delaware executed a search warrant at Nathaniel Greenlee's residence in Delaware. When Delaware state troopers breached the front door, Nathaniel Greenlee's father, John Greenlee, shot one of them, according to authorities.
John Greenlee was arrested by Delaware State Police. The trooper was released from the hospital that day.
On the same day, detectives discovered that Nathaniel Greenlee was employed by a large retail store in Concord Township, Pennsylvania. They found his car, which is believed to have been used in the crime, at the store and arrested him.
On Aug. 8, Donavon Jackson, 20, of Wilmington, Delaware, was arrested at home. Authorities said they found cash believed to be a part of the stolen currency and property purchased with proceeds from the crime.
On Aug. 13, Myles Coleman, 23, of Atlantic City, surrendered to detectives in Atlantic City. According to detectives, Evans, Greenlee, and Jackson went to Coleman's residence immediately after the robbery.
Plummer, Evans, Jackson and Morgan were being held in the Atlantic County Jail on robbery, assault and weapons charges. Greenlee is awaiting extradition from Pennsylvania on similar charges. The other three suspects were released with a future court date on a charge of receiving stolen property.
Wayne Parry can be reached at http://twitter.com/WayneParryAC