A Bergen County couple has been charged with murder after their 4-month-old son died in a Burlington County motel room while they smoked cigarettes outside.

William Herring, 42, and Brianna Brochhausen, 22, of Mahwah, had previously been charged with endangering the welfare of a child, but their charges were upgraded to murder on Tuesday, Burlington County Prosecutor Scott Coffina said in a news release.

Their son Hunter stopped breathing at the Hilltop Motel in Springfield on Valentine's Day.

Investigators learned that the couple, frustrated that Hunter would not stop crying, put him on his stomach on a bed in the motel room. Then, they pulled the comforter over him, covering the baby's whole body, including his head.

The parents then smoked cigarettes outside the room for about 10 minutes. When they came back into the room, Hunter was not breathing.

He was taken to Virtua Memorial Hospital in Mount Holly and then transferred to the Pediatric Intensive Care Unit at the Children's Hospital of Philadelphia, where he had little brain activity and needed a respirator to breathe. Hunter died March 3 when he was taken off life support.

A Philadelphia medical examiner said the baby died from suffocation.

New Jersey State Police arrested the couple yesterday, and Superintendent Col. Patrick Callahan commended investigators "for their commitment and dedication to finding justice for Baby Hunter."

The parents' "thoughtless actions...ended up costing a defenseless 4-month-old infant his life," Callahan said.

Coffina wants to remind parents of a 24-hour "stressline" to hear concerns and crises at 1-800-THE-KIDS or www.pofnj.com. The state also has the Safe Haven Infant Protection Act, which allows parents or their representatives to anonymously surrender a newborn baby at hospitals or other emergency stations that are staffed 24/7.

"The responsibilities of becoming a new parent can sometimes be overwhelming," Coffina said. "Those who find themselves at a point of crisis when caring for a newborn child should know that help is available, and they must seek that help rather than taking actions that might harm their child."

Herring and Brochhausen will appear in Superior Court in Mount Holly later this week for a detention hearing.

Joe Brandt can be reached at jbrandt@njadvancemedia.com. Follow him on Twitter @JBrandt_NJ. Find NJ.com on Facebook. Have a tip? Tell us. nj.com/tips