A massive search effort for a suspect wanted for shooting a Florida deputy during a traffic stop entered its fourth day Monday, as the reward for the gunman’s capture was once again upped and schools in the northeastern-most part of the state remain on modified lockdown. 

The reward for 35-year-old Patrick McDowell’s capture is now $54,000, the Nassau County Sheriff’s Office said, warning the man could still be in the area and residents should not drop their guard. Anyone who sees anything out of the ordinary is advised to call the sheriff’s office at 904-225-5174.

The sheriff’s office advised residents that there would be a heavy police presence in the Sandy Ford Road at US 301 area of Callahan on Monday that would include about 200 vehicles and deputies, as law enforcement members from several agencies scour a 5-square-mile area. 

FLORIDA PROSECUTORS SEEK DEATH PENALTY FOR FORMER MARINE ACCUSED OF KILLING INNOCENT FAMILY IN ‘RESCUE’ OP 

"Do not be alarmed. We are collecting evidence," the agency said on Facebook. "We don't know how long this will take. Thank you for your patience." 

McDowell, who reportedly served in the Marines, is accused of shooting Nassau County Deputy Josh Moyers during a traffic stop on Friday. Moyers, 29, died at 2:19 p.m. Sunday at UF Health Jacksonville. A weapons expert who trained McDowell as a security guard about a decade ago described him as a "survivalist" with military experience and skills to hide himself in the woods, WJXT reported. 

Patrick McDowell (left) is accused of shooting Nassau County Deputy Josh Moyers during a traffic stop on Friday. Moyers died at the hospital Sunday. 

Patrick McDowell (left) is accused of shooting Nassau County Deputy Josh Moyers during a traffic stop on Friday. Moyers died at the hospital Sunday.  (Nassau County Sheriff's Office)

"Please keep Josh’s family and fiancé in your thoughts and prayers as we navigate this terrible tragedy," Nassau County Sheriff Bill Leeper said in a statement. Footage captured Moyers’ procession from the hospital, as a fire rescue ambulance transported his body to the medical examiner’s office. 

Sheriff Leeper on Monday morning swore in law enforcement members from the Camden County Sheriff's Office, Georgia State Patrol, Georgia Department of Natural Resources and Charlton County, giving them authority to make an arrest in Nassau County.  

Deputies had gone door to door to check on residents over the weekend amid their search. The sheriff’s office has been circulating several photos of the alleged "cop killer," who was last seen wearing a black T-shirt, white under shirt, camouflage shorts, and black shoes. McDowell has a tattoo on his left shoulder that reads "Death Before Dishonor" and a tattoo on his right arm that reads "EGA." 

CLICK HERE TO GET THE FOX NEWS APP

Nassau County School District Superintendent Kathy Burns instructed Callahan Middle School, Callahan Intermediate, West Nassau High School, as well as other schools nearby to operate on a modified lockdown basis on Monday amid the ongoing manhunt, meaning students will not change classes. Although buses will run, absences will not be counted for students whose parents have them stay home.