EVERETT — Police were investigating a homicide in an apartment after a man’s body was found there Saturday in an “advanced state of decomposition,’’ the district attorney’s office said.

The man, who was believed to be in his 60s, was found by his landlord at 25 Oakland Ave. during a well-being check, according to a statement from the district attorney.

Investigators have not determined what day the man died, and the medical examiner’s office is working to identify him.

Meghan Kelly, a spokeswoman for district attorney’s office, said Monday night that “because of the state of decomposition,’’ authorities will not confirm the man’s name until the medical examiner’s office has a definite identification.

The street, which is lined with multifamily and single-family homes, was quiet Monday night. About six men arrived shortly after 8:30 p.m. and entered the three-story home, many wearing gloves and carrying bags. Shortly after, one could be seen through a second-floor window, examining a piece of clothing.

One resident on the street said she last saw the man who lived in the apartment about 10 days ago. “Just a really sweet guy,’’ said that next-door neighbor, Lisa D’Ambrosio.

He had invited D’Ambrosio to come upstairs to his apartment to have dinner together and look at his artwork. His art was a big part of his life, she said, and something he proudly told her about.

“He invited me up several times to see his artwork, and I never did,’’ she said. “I’m really disappointed because he was a really, really nice guy.’’

D’Ambrosio said she often saw him walking outside with a young man, whom she believed to be his son. She said the man also enjoyed sitting on his deck when the weather was warm.

Garvens Florus, who lives a couple houses down, also said his neighbor often walked outside with a man Florus believed to be his son. “We never really talked to them,’’ he said, “but they were always friendly.’’

Felicia Gans can be reached at felicia.gans@globe.com.