Image copyright Police handout Image caption Howell Donaldson, 24

A McDonald's employee has been arrested in the US state of Florida on suspicion of being a serial killer.

Howell Emanuel Donaldson III is accused of randomly killing four people between 9 October and 14 November in Tampa.

The 24-year-old was detained on Tuesday afternoon at a branch of the burger restaurant where he had reportedly worked for two months.

He had asked a manager to hold on to his loaded 9mm handgun, the Tampa Bay Times reports.

Police say the suspect had "expressed his intention to leave the state".

Image copyright AFP Image caption Memorials in honour of the victims have appeared throughout parts of Tampa

Another McDonald's employee noticed a police officer filling out paperwork in the restaurant, and urged her manager to tell the officer about the gun.

Police believe the gunman chose his victims arbitrarily and a motive is still unclear.

Mobile phone records indicate Mr Donaldson was in the area of three of the murders, according to a sworn police affidavit.

He admitted legally purchasing the pistol on 3 October, say police.

Media playback is unsupported on your device Media caption SWAT team searches Florida neighbourhood for serial killer

Investigators say the Glock handgun has been tested and matches bullet shell casings recovered from the murder scenes.

Police say that clothing found during a search of Mr Donaldson's car looks like that worn by a man captured on homeowners' CCTV footage near the crime locations.

They add that the clothes appear to be stained with blood.

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The killings left many residents of Tampa's working-class neighbourhood of Seminole Heights afraid to venture out after dark.

Police accompanied students to bus stops, while protesters held reclaim-the-streets demonstrations.

All four victims were either boarding or disembarking from a bus at the time they were shot:

Benjamin Mitchell, 22, a musician, was killed on 9 October while waiting at a bus stop

Monica Hoffa, 32, a waitress, was gunned down on 11 October while walking to meet a friend

Anthony Naiboa, 20, a mild autism sufferer, was fatally shot on 19 October while walking home from work

Ronald Felton, 60, a construction worker was killed on 14 November

Mayor Bob Buckhorn told a news conference after the arrest: "Fifty-one days ago, I said this was a struggle between good and evil.

"Well tonight, goodness has won. Tonight, in the battle between darkness and light, light has won."

Image copyright Tampa Police Image caption Police had asked for help identifying this person who was seen near the crime scenes

Florida Governor Rick Scott visited police in Tampa on Wednesday to thank them for the investigation.

"In Florida, we have absolutely zero tolerance for this type of evil behaviour," he said, vowing justice for the victims.

The FBI helped police in the investigation.