The homicide ruling could prompt new charges of murder or manslaughter against Mark Kerrigan, legal experts said. Prosecutors could charge murder if there is evidence that he intended to kill his father, or manslaughter if it is determined that his acts were reckless enough to lead to death.
Both would require proof that Mark Kerrigan's alleged attack caused his father's death. Despite the homicide ruling, cause of death would ultimately be decided by a jury.
"I am guessing there will be a battle between medical experts on both sides," criminal defense lawyer David Duncan said.
"The prosecution will have an uphill battle because of the inability of any medical expert to define the actual cause of death without engaging in speculation," according to Veronica J. White of White & Associates, P.C.
Kerrigan's pre-existing heart condition makes causation even harder to prove, White added.
The Middlesex district attorney's office would not comment on whether it will bring new charges, saying only that the investigation "remains ongoing."
Mark Kerrigan is being held at Bridgewater State Hospital, where he is undergoing psychiatric evaluations. He is scheduled to be back in court for a probable cause hearing on Feb. 24.