What to Know NYPD vehicles were seen leaving a Pennsylvania landfill Monday, and sources say they're searching for missing man Michael Stewart

The 40-year-old Staten Island father was last seen on Dec. 20, and he's been presumed killed

Police sources say a couple he knew are considered persons of interest in his presumed death

The NYPD has traveled to a Pennsylvania landfill in their ongoing search for a missing Staten Island father who has been presumed dead, law enforcement sources say.

Law enforcement sources confirmed Monday the NYPD was searching the Republic Service Conestoga Landfill, about 140 miles from New York City, in connection with the disappearance of Michael Stewart.

The 40-year-old father of two was last seen on Dec. 20, and he last sent a text message to his mother on Dec. 21, writing, "Please help me Mom," the New York Post reported.

An army of @NYPD vehicles was spotted Monday afternoon at the Exxon station in #Morgantown. They were leaving from an investigation being conducted at the @RepublicService Conestoga Landfill. @PAStatePolice are also on the scene. pic.twitter.com/PmKvxYM8hH — Michael Yoder (@YoderReports) January 7, 2019

A reporter at The Reading Eagle first spotted NYPD vehicles, along with Pennsylvania state police, leaving the landfill Monday evening.

Stewart was seen on surveillance video Dec. 20 horsing around with his friend Angelo Nesimi inside a barber shop in Port Richmond. Nesimi is a person of interest in Stewart's disappearance, the Staten Island Advance reported.

Nesimi, 33, was arrested Dec. 31 in connection to a violent attack on his girlfriend, Zammara Sanchez, police told the Post. The couple were previously questioned in the suspected killing of Stewart, and Sanchez told detectives that her boyfriend "killed somebody -- and he made me go with him to get rid of the body in New Jersey," the Post reported, citing sources.

Investigators believe it's possible that Stewart's body was dumped in New Jersey, and that sanitation workers may have picked it up with the trash and it was incinerated, the Advance reported, citing a source. Another source said surveillance video shows Nesimi and Sanchez tossing what could be a body into a Dumpster in Perth Amboy, New Jersey, before driving away in a Chrysler sedan.

Sources also told the Post that Stewart had a relationship with the couple: "It was a relationship between the three of them that ended with [Stewart] stabbed up," a police source told the Post.

Nesimi told the Daily News in a jailhouse interview this month, "I didn't do it, 100 percent. They're trying to pin it on me."

Both Stewart and Nesimi have criminal records. Nesimi claimed he knew Stewart only for the past few years and that they kept up with each other because they went to the same barber shop, but said they weren't close.

No one has yet been charged in the suspected killing, and a body has not been found.