A popular English professor at Farmingdale State College was decapitated by her mentally ill son in their apartment Tuesday before he killed himself by stepping in front of a Long Island Rail Road train, police said Wednesday.

The remains of Patricia Ward, 66, who taught at the college for 28 years, were found in the roadway outside the Farmingdale apartment she shared with her son Derek Ward, 35, on Secatogue Avenue, about 8 p.m., police said. Her head lay near her torso, police said.

Detectives believe Ward killed his mother in the second-floor residence, cut her head off and dragged her remains into the street. He had a 10-year history of psychiatric issues, which were worsened by the death of his paternal grandfather in September 2013, police said.

"Her body was removed from the apartment by, we believe, her son Derek and placed in the street," said Nassau Police Det. Lt. John Azzata, commander of the department's homicide squad.

A knife found in the apartment may be the murder weapon, Azzata said, adding that Patricia Ward suffered "broken ribs and multiple stab wounds."

No domestic disturbances involving the mother and son were ever reported at the apartment, and neighbors heard nothing unusual during the crime, police said. The Wards had moved there from Babylon about three months ago, police said.

Patricia Ward was last seen alive some time after 4 p.m. Tuesday. Her remains lay in the street around seven minutes before police were called and responded about 8 p.m., Azzata said.

Derek Ward was struck by an oncoming LIRR train between a quarter and a half mile away from the scene at 8:20 p.m., police said.

His criminal history consists of two convictions, police said: one in 2003 for criminal mischief, for which Ward received a sentence of 1-year probation and a fine; and another in 2006 for gun and drug possession.

In the latter case authorities said they found Ward carrying a 9-mm Smith & Wesson and 100 Valium pills. He was sentenced to 45 days in jail and 3 years' probation, police said.

The murder-suicide rattled residents in Ward's neighborhood and left her students and colleagues at Farmingdale State College in mourning.

An assistant professor of language arts, Ward, who was divorced, taught at the college's Long Island Educational Opportunity Center, helping high school students prepare for college.

"She was well-liked, well-known and well-respected," said Patrick Calabria, vice president of institutional advancement at the college. "It's a tough day here. She was very passionate and devoted and loved working with students."