Lannon is accused of breaking into 66-year-old Michael Dabkowski’s home and beating him with a blunt object on Monday, according to an affidavit.
Officers performing a well-being check found Dabkowski’s body, according to the prosecutor’s office.
Lannon is also a person of interest in the death of his wife and three others in New Mexico.
Authorities say a vehicle was discovered last week at the Albuquerque International Sunport garage with four bodies later identified as Jennifer Lannon, 39, Matthew Miller, 21, Jesten Mata, 40, and Randal Apostalon, 60. Sean Lannon lived 80 miles (130 kilometers) away in Grants, New Mexico.
Grants Police had posted on Facebook last month that they were seeking a different person in connection with the disappearances of Jennifer Lannon, Miller and Mata. Authorities did not offer further information about that potential suspect on Wednesday.