MOLUNKUS TOWNSHIP, Maine — A convicted sex offender whose body police found in his Macwahoc Road home in March died from being forced to overdose on his own medications, officials said Friday.

Lawrence Lewis, 68, died of “acute intoxication due to the combined effects of Risperidone [an antipsychotic] and nitroglycerin,” a spokeswoman for the state medical examiner’s office said Friday. The manner of death is labeled a homicide.

The results confirm the story that Bruce Neal, aka Bruce King, told Penobscot County Sheriff’s Deputy Patty McLaughlin shortly before he killed himself on March 11, said Stephen McCausland, spokesman for the Maine Department of Public Safety.

“We have more work to do in this case, but the early suspicion that we were dealing with, that this was a murder-suicide, is correct. He [Lewis] was forced to consume these drugs and died from that,” McCausland said Friday. “This investigation is not over. There is some additional work to do.”

King, 59, was involved in a four-hour standoff with police in a U-Haul truck on Interstate 95 just south of Lincoln that ended when he used a .30-30 rifle to kill himself.

During the standoff, King said that he had killed Lewis by forcing him to take medications prescribed to Lewis — two bottles of nitroglycerin tablets and a bottle of psych meds — because he believed that Lewis had been molesting children. King then hid the body inside Lewis’ house in Molunkus, state police have said.

Lewis, 68, was on the state’s sex offender registry for life after having been convicted in 1996 of sexually assaulting a 9-year-old boy.

King’s claims might have been a sham. He was being investigated for a sex assault in Maine that allegedly occurred in January. State police learned days after his suicide that King was on the sex offender registry in Massachusetts for a rape in 1985.

“It is a bizarre case that we have not seen the likes of in awhile. I have stopped saying ‘never,’ but this is a very unique case,” McCausland said.

Listed as an atypical anti-psychotic, Risperidone treats schizophrenia in adults and teenagers age 13 years and older. It lessens episodes of mania or simultaneous symptoms of mania and depression in bipolar disorder cases, according to the MedlinePlus website, a service of the National Institutes of Health.

A vasodilator, nitroglycerin reduces angina or chest pain in cases of coronary artery disease, the narrowing of the heart’s blood vessels. It relaxes the vessels to ease the heart’s workload, according to MedLinePlus.

Lewis’ friends have said that the man was a victim of a homicide, not just a sex offender, who had worked diligently to prove his innocence of the sex assault charges.

State police received on Thursday the results of the toxicology tests done at Lewis’ autopsy, McCausland said.

McCausland said that one key witness to the event was King’s wife of 10 days, Lynda Dube.

Dube, who fled the U-Haul truck when the standoff began, told state police that the couple was leaving a Medway motel that day when King saw a police officer — apparently investigating Lewis’ disappearance — and pointed the .30-30 rifle at her. The rifle belonged to Dube’s ex-husband, who gave it to her, the ex-husband’s father has said.

“The main suspect in this case is dead,” McCausland said in reference to King. “She has cooperated with law enforcement since she started giving us information on the interstate. We have interviewed her extensively.”