MIAMI -

Police on Sunday arrested an 18-year-old man accused of killing a security guard at a southwest Miami-Dade apartment complex.

Police charged Quintin Vicks with first-degree murder and armed robbery. When he was arrested, Vicks was on probation for possession of marijuana.

According to police, Vicks and some other teenagers ambushed Robert Nelson, who was inside his car patrolling the apartment complex at Southwest 137th Avenue and 207th Street late Saturday, shooting him several times. They killed him and stole his gun.

Nelson was pronounced dead after being transported to Kendall Regional Trauma Center.

Police found Vicks with Nelson's credit cards, money and ID, police said, in a nearby parking lot. A judge denied Vicks bond Monday.

Nelson worked for North Miami-based 50 State Security.

"It's devastating and it's not something that you can ever prepare for," said 50 State Security President John Williams. "He's a great, great guy, very cordial, very friendly. The feedback from a lot of people [is] that he was somebody who made them laugh all the time, he was always making jokes and having fun."

Police have since arrested three others: 27-year-old Gregory Lewis, 19-year-old Malik Mills, and 19-year-old Nathaniel Payne Collins.