Jurors on Friday convicted a 43-year-old man of first-degree murder in the killing of his girlfriend, who died in her seat on an overnight train to Denver nine years ago.

The Denver jury affirmed prosecutors’ theory that Angelo Mantych killed 28-year-old Marina Placensia on an Amtrak train before it rolled into Union Station early in the morning on Sept. 1, 2016 — a trip witnesses said she took in an attempt to leave him and escape their long-abusive relationship.

The jury found that the murder was an act of domestic violence.

Mantych dropped his head when the verdict was read. He will be sentenced to life in prison without the possibility of parole.

Placensia had planned to rely on her family in Denver to separate from Mantych after she arrived, Assistant District Attorney Lara Mullin told jurors during closing arguments in Denver District Court on Friday morning.

“He knows what is waiting at that train station is a collection of family members who are going to make sure he doesn’t go home with Marina and the boys,” she said.”…Because things were at a breaking point and people knew it.”

Jurors heard about Mantych’s long history of domestic violence against Placensia during the two-week trial, and that Placensia made a plan to move to Denver from Wisconsin to get away from her boyfriend, the father of three of her children. Witnesses testified that Placensia tried to keep the plan secret from Mantych and that he was not supposed to join them on the train trip.

Mantych discovered the plan at least two days ahead of the train’s departure, Mullin told jurors, and then joined his family on the trip.

Prosecutors alleged Mantych silently suffocated Placensia in her seat on the train during the night before it reached Denver, steps away from their children and without anyone noticing. Mullin told jurors that the train was not full — there were 79 empty seats — and played a video showing a dark train to try to explain why no one witnessed the killing.

Mantych told officers he tried to wake his girlfriend about 20 minutes before they arrived in Denver, and assumed she was sleeping deeply when she did not stir. He said he tried again 10 minutes before arrival and then sought help when she still did not respond, according to an affidavit.

Defense attorneys argued the woman died of natural causes, potentially including liver and heart conditions complicated by withdrawal from alcohol.

“It really is something that brings a lot of reasonable doubt to this case,” public defender Srinija Pernankil said during closing arguments. “It is an area that was uninvestigated, and that is very important to consider.”