Transcript for How Tampa police tracked down alleged serial killer at a McDonald's
Today the light shines. The darkness is over. This community begins the healing process. Reporter: A sigh of relief in Tampa today after an arrest was made in connection to four unsolved murders that have terrorized this community for nearly two months. For 51 days we had a neighborhood that was held hostage. Reporter: Benjamin Mitchell, 22. Monica Hoffa, 32. 20-year-old Anthony naiboa. 60-year-old Ronald Felton. All seemingly unconnected members of this community shot and killed in a series of murders that confounded authorities. Yesterday, 24-year-old Howell Donaldson III, a former St. John's university student, was brought in for questioning, picked up outside of this McDonald's where he worked after police received a tip from a co-worker. He told my boss to hold his book bag for him. He said, don't go in the book bag, whatever you do. She went in the book bag, she found a gun. After finding the gun she called police. Reporter: This gun police say was the missing link leading them to Donaldson. That firearm was used in all four murders. As our investigation continued into the early hours of this morning, we were then able to gather the probable cause and charge Howell Donaldson with four counts of first-degree murder. Reporter: Police say Donaldson admitted to owning the weapon which authorities say was bought legally, but has not confessed to the killings. He was cooperative. But he did not tell us why he was doing this. We were really hoping to find out what was driving him to do this. We don't have those answers yet. Reporter: Authorities also point to Donaldson's cell phone records linking its location to the cell tower closest to three of the homicides. Donaldson is set to make his first court appearance tomorrow morning. The string of murders has had this community on edge for weeks. Can we talk about how strange this is for something like this to happen, how unnerving, how scary it is? It's the first time that anything this horrific has happened. I just bought it. Now is the time. Got to protect my family. Never seen this many police officers, actually. It's unsetting but it's settling. Reporter: The murders forced authorities to rely on tips from the community. Soliciting tips is not a preferred choice of law enforcement. Usually you're in a bind because you've run out of leads or the leads that you have have gone into a dead end. So you solicit whatever information you can get. Reporter: Chief David brown has been in this bind before. For six years he led the Dallas police department. A unit that lost five cops last year when an armed gunman ambushed his officers. He knows all too well the importance and difficulty in gathering information from the community. Tips are important, because they can corroborate evidence found at the crime scene. They can provide a missing link to a puzzle that you're trying to resolve. Reporter: In this case, Tampa law enforcement say they received more than 5,000. According to authorities, the killing spree began on October 9th. 22-year-old Benjamin Mitchell shot while waiting alone at a bus stop. Four days later -- She didn't have a chance to get married. Reporter: The body of 32-year-old Monica Hoffa found in an empty lot down the street around the corner from the scene where Mitchell was killed. Monica's uncle devastated. Loved everything. Her interest was community. And the deaf community. She loved everybody. Reporter: Their suffering rocked the community. We don't want Monica to be forgotten. Reporter: Six days after Hof Hoffa's death, a third murder, 20-year-old Anthony naiboa. It sounded really close. Like five minutes after that, the paramedics came. Reporter: He was a recent high school graduate who had autism. Police say he was killed while on his way home from work. I can't imagine how difficult this is right now. Reporter: His family heartbroken. Whoever did this is, it's turned life upside down. It's a shame that I won't be able to see him no more, talk to him no more. Reporter: A fourth victim, 60-year-old Ronald Felton, D the homeless. I love him but he's still going to Ben me, he's going to be in my heart. Reporter: Police point to the fact that eh victim was gunned down within a half mile of each other. They say in each shooting the victim was alone but none were robbed. Before yesterday's tip leading to Donaldson's arrest one of the main leads authorities had were grainy surveillance videos of who they called a suspect. Today community members and families of the victims welcome the arrest of the alleged killer. Thank god we got this guy. We got this guy. Reporter: Embracing one another with cautious optimism that the dread of the past two months may finally be over. We call it a group hug. When everybody comes together, that's a group hug. That's when we all become one. And it was all just letting our spirits go together. Reporter: For "Nightline," I'm Victor Oquendo in Tampa, Florida.
This transcript has been automatically generated and may not be 100% accurate.