A $100,000 reward is being offered for a tip that leads to an arrest in the case.
"We have a gun", said Dugan.
The tip that led police to him came from one of his co-workers at an Ybor City McDonald's, which is near the Seminole Heights neighborhood.
"It's been a long time for the families and for the cops, and so I'm guarded on the whole thing, but I'm optimistic", Dugan said, adding it would be a long night for police.
The employee said the co-worker handed a manager a gun and left to visit an Amscot.
Investigators found a.40-caliber handgun inside the bag, the same weapon that has been used in all four murders, police told Bay News 9.
The man is being questioned by police, but he's not in custody or under arrest.
Days later, the body of Monica Hoffa, 32, was found in a vacant lot on East New Orleans Avenue, about a half-mile from where Mitchell was shot.
It's been 51 days since Donaldson claimed his first alleged victim - 22-year-old Benjamin Edward Mitchell at a bus stop near his home in Seminole Heights Oct. 9.
The cop called for backup and officers took Donaldson in for questioning when he returned.
A third man, 20-year-old Anthony Naiboa, was gunned down October 19 - just 200 yards from where Mitchell was found shot.
Howell Emanuel Donaldson III, 24, graduated from St. John's in January 2017, after enrolling there in the fall of the 2011, university officials confirm to News 4. "Well, tonight goodness has won".
"We have recovered other firearms before so we will see", Dugan said. Police said 60-year-old Ronald Felton was crossing the street when someone shot him from behind.
It's not clear why Donaldson picked the southeast Seminole Heights neighborhood of Tampa to choose his targets, but Dugan said he always believed the killer was familiar with that neighborhood.
More than 5,000 tips have poured into police and Crime Stoppers since the murders were announced, according to WFLA.
The four killings happened within a month, all of the victims were alone when they were shot.