John Arnold Jr., the son of a Newark police lieutenant and himself a law enforcement veteran, has filed to run in the June Democratic primary for Essex County Sheriff, a post held for decades by fellow Democrat Armando Fontoura.

His campaign announced the filing today and the Essex County Clerk’s Office confirmed it. No other candidate, Democrat or Republican, has yet filed to run in the primary, the clerk’s office also said.

Arnold, who was profiled by Patch in December, has served in law enforcement since 1985, when the Science High School alumnus became an officer with the campus police at the University of Medicine and Dentistry in Newark.  The Marine Corps veteran went on to become a detective with the Essex County Prosecutor’s Office, where he was the first African-American lieutenant in the homicide division and the first to be named commander of that division.

Married and a father of four, Arnold, 46, said that if elected, he would work to raise the profile of the sheriff’s office, whose responsibilities include patrolling county parks, serving as court officers and running specialized units such as the bomb squad.

He would also expand the deputy program, in which civilians receive training and supplement the paid force, and promised to make the force more diverse to reflect the community it serves.

Fontoura, 69, who has served as sheriff since 1990 and plans on seeking an eighth three-year term this year, will likely be a formidable opponent. In both the 2006 and 2009 Democratic primaries, he handily defeated challengers Janice Matos and Richard Mastrangelo, respectively. Fontoura then cruised to victory in both general elections.