The Nassau County Sheriff's Office arrested Skyler Cole Johnson, 24, on suspicion of killing his mother's boyfriend.
A Sheriff's Office investigation revealed Johnson's mother and her boyfriend, Richard Benjamin Crews, 38, from Hilliard, Florida, were arguing over household finances, NCSO said.
Johnson heard the arguing from inside his home and went outside to find his mother underneath a truck. Johnson shot Crews several times with a 9 mm handgun, authorities said in a report.
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Johnson unloaded the weapon and placed it on the trunk of a white vehicle that Crews was trying to leave in, the report said. Johnson then called 911 to report what happened.
NCSO deputies and Nassau County Fire Rescue responded, and Crews was transported to UF Health in Jacksonville and pronounced dead at 1:20 p.m.
After several witnesses were interviewed, Johnson was arrested on suspicion of second-degree murder and transported to the Nassau County Detention Center.
The shooting is still under investigation, according to NCSO.