Cops to suspected serial killer: 'We know it's you. Can you please tell us why?' A suspected serial killer told cops he gave gun to his boss for safekeeping.

While they didn't get a confession, Florida cops got a suspect to give them all the evidence they said they needed, including the murder weapon, to link him to a series of killings that terrorized a Tampa neighborhood for 37 days in 2017, according to investigative reports and an audio recording of the interrogation.

Howell Donaldson III, a former member of the St. John's University men's basketball team, was arrested after four hours of interrogation by Tampa Bay police detectives after police said he gave them permission to test his handgun and inspect his iPhone.

Tests on the gun confirmed the weapon was used in the killings in the Seminole Heights neighborhood of Tampa, and data on Donaldson's cellphone showed he had been in the neighborhood at the times of all four killings, according to records and audio recordings released by prosecutors on Friday.

Donaldson was detained for questioning on Nov. 28, 2017, after he brought a duffel bag containing a loaded .40-caliber Glock 27 handgun to work at a McDonald's and tried to give it to his manager for safe keeping. The manager called the police, giving them the key break in solving the serial killings that began Oct. 9, 2017, when Benjamin Mitchell, 22, was shot while waiting at a bus stop.

In an audio recording of the interrogation obtained by ABC station WFTS-TV in Tampa, Donaldson told homicide detectives Kenneth Nightlinger and Austin Hill why he tried to give his legally purchased gun to his manager at McDonald's.

"I was going back to St. John's, and I didn't want the firearm to be in my home with my little brother. Accidents happen," Donaldson told the detectives.

But the detectives didn't believe him, and Nightlinger asked, "Was that something that was driven by your conscious, to make sure that you did not have that gun in your possession? Was it a conscience-driven act?"

Donaldson simply replied, "Nah."

During the interrogation, the detectives spoke with Donaldson on topics ranging from basketball to the education he was pursuing at St. John's in Queens, New York, before they began grilling him about the series of unsolved killings. The school confirmed Donaldson had been a walk-on member of the men's basketball team briefly during the 2011-12 season.

Nightlinger went through each killing with Donaldson, showing him photos of the victims, calling them "decent people."

"That's a 60-year-old man that was out feeding the homeless. That's an autistic kid, OK, that missed his bus. This young woman, 30 years old, was merely walking from her aunt's place. All right? Just down the road, in her neighborhood. And this young man right here was waiting at a bus. To go pick up his girlfriend and make sure she got home safely," Nightlinger said in the audio tape. "Decent people. People like you."

The detective continued, asking Donaldson, "What makes a person do that? Is it something in their mind that just snaps?"

Donaldson responded, "I don't know. Probably lost a loved one, or, I don’t know."

At that point, the detectives pressed harder, asking whether he had lost a loved one. Donaldson told them he had an aunt he was close to who had died of cancer.

As the grilling continued, the detectives questioned Donaldson about the serial killings and asked if he owed the victims' families an explanation. They told Donaldson the tests on his gun would soon come back, possibly confirming their suspicions that he was involved in the killings.

"The times these people were killed, you were up in that area. But you haven't told me as to why. Can you explain why?" Nightlinger asked, telling Donaldson his cellphone data and searches connected him to the location of the killings around the times they were committed.

In addition to Mitchell, Monica Hoffa, 32, was shot to death on Oct. 11; Anthony Naiboa, 20, was gunned down on Oct. 19; and Ronald Felton, 60, was fatally shot on Nov. 14.

"Can you explain why you did a number of searches on the Seminole Heights case?" Hill asked the suspect.

Donaldson declined to answer, saying, "I just want to see my family right now."

"This is the gun. You murdered those people. Your phone put you right there at specific times," Nightlinger said. "We know it's you. Can you please tell us why?"

Donaldson replied: "I just don't know anything else to say. I just want to ... I guess talk to my attorney, or talk to who I need to talk to."

Soon after the interrogation ended, Donaldson was arrested on suspicion of four counts of murder, and he was later indicted by a grand jury.

Donaldson's parents, Howell Jr. and Rosita Donaldson, also spoke to detectives.

"We wondered why he didn't go out and do things with friends, but he was always home," Rita Donaldson told detectives, according to police documents obtained by WFTS.

She was asked if they'd noticed a change in her son.

"Some the last couple of months," she said, "but nothing like this."

When the parents later refused to answer questions from prosecutors, Circuit Judge Mark Wolfe in February found them in indirect civil contempt of court. Wolf ordered them placed under house arrest.

Prosecutors said they will seek the death penalty against Donaldson, whose trial has yet to be scheduled.