JACKSONVILLE, Fla. -- Police have arrested two men on charges they killed two people -- one a 16-year-old boy -- on the morning of July 20.

At the beginning of what Jacksonville Sheriff's Office homicide Lt. Pat Ivey called a "violent crime spree," 39-year-old Patrick Stafford was shot and killed just before 6 a.m. during an attempted robbery in the front yard of a relatives house on Academy Street.

Just over four hours later, 16-year-old Monquell Wimberly was riding his bicycle on King Street when he was shot and killed from someone in a passing car.

Ivey said witnesses identified the car from which the shots were fired as one taken in a carjacking at a business at Tyler and Beaver streets that occurred between the two slayings.

Surveillance video of the carjacking along with witness statements provided police enough evidence to obtain warrants charging Rashard Evans, 20, and Billy Sheppard, 22, with first-degree murder.

Asked what motivated the shootings, Ivey said, "just plain meanness."

These slayings and two others occurred on the same day, prompting some city officials to call it "bloody Sunday." The following day, Sheriff John Rutherford said he needed a surge of new police officers to fight escalating violence in Jacksonville.

Sheppard has previous convictions for aggravated battery with a firearm, possession of a firearm on school property and being a convicted felon in possession of a firearm. He went back to prison when he violated probation and got out in February 2007.

Police said Evans also has a history of arrests on violent offenses, including armed robbery, carjacking and possession of a firearm by convicted felon.

Both were being held without bond in the Duval County Jail.