Denver, Colorado – Nearly nine years after a young mother was found unresponsive aboard an Amtrak train, a Colorado jury has found Angelo Valentino Mantych, 43, guilty of first-degree murder for killing his girlfriend, 28-year-old Marina Placensia, as their children slept nearby.
Mantych was convicted on Friday following a case that remained unresolved for years due to initial uncertainty surrounding Placensia’s cause of death. Prosecutors argued that Mantych strangled and suffocated her during the overnight train ride in August 2016, as she was preparing to leave an abusive relationship.
What happened on the train
Placensia, Mantych, and their four children were traveling from Racine, Wisconsin, to Denver, where family members were waiting to help Placensia separate from Mantych. When the train arrived at Denver Union Station, Placensia was unresponsive.
Emergency responders attempted resuscitation, but she was pronounced dead at the station. At the time, Mantych told authorities he believed she was a “heavy sleeper” and claimed he unsuccessfully tried to wake her multiple times before realizing something was wrong.
According to investigative documents, officers observed Mantych crying, vomiting, and appearing distressed. No passengers reported witnessing a fight or disturbance during the trip, complicating the initial investigation.
Years without charges
An early autopsy revealed numerous bruises across Placensia’s body, including injuries to her face, mouth, thighs, calves, abdomen, and fractured ribs. However, medical examiners could not immediately determine a cause or manner of death.
Mantych offered multiple explanations for her injuries, telling investigators they occurred during the move, from doors striking her, or from interactions with their young children. With no clear forensic conclusion, the case stalled for years.
Prosecutors reveal motive
The case was revived after a follow-up forensic review in 2025, when a medical expert concluded that Placensia died from suffocation caused by pressure to her face and obstruction of her nose and mouth. The doctor determined the manner of death was homicide, ruling out medical or accidental causes.
Prosecutors argued Mantych knew Placensia intended to leave him once they reached Denver.
“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,” Assistant District Attorney Lara Mullin told jurors, according to court reports. “Things were at a breaking point.”
They said Mantych killed Placensia in her seat during the night while their children slept nearby, unnoticed by other passengers.
Evidence of long-term abuse
Testimony painted a disturbing picture of years of domestic violence. Neighbors described frequent assaults, including one witness who said Mantych “beat” Placensia the day before they left Wisconsin. Another neighbor told investigators Mantych physically abused her nearly every day.
Witnesses reported seeing Mantych slap, punch, choke, and pull Placensia’s hair during the move. He allegedly shouted insults at her and ordered her to move furniture faster while yelling at the children.
Several witnesses also described abuse directed at the children. One recalled hearing a child plead, “please stop, it hurts,” followed by Mantych allegedly telling the boy to “take it like a man.” Another said the children appeared trained not to speak up.
Investigators also uncovered prior assault allegations, including a 2015 incident in which Mantych allegedly punched Placensia in the head multiple times, causing hearing damage. Friends said she often wore sweaters and sunglasses in summer to conceal injuries.
Chilling threats and control
Court documents revealed Placensia feared for her safety. In one reported incident, Mantych allegedly threatened to throw a baby off a balcony if she did not comply with his demands. In another, she told witnesses he struck her sexually during an assault.
When Placensia planned to leave him, Mantych allegedly told her, “If I can’t have you, no one will.”
Verdict and sentencing
Jurors deliberated for about five hours before returning a guilty verdict. Mantych is scheduled to be sentenced on January 9, where he faces the possibility of life in prison.
A tragic end after trying to escape
Prosecutors emphasized that Placensia was attempting to protect herself and her children when her life was taken. The case underscores the dangers victims face when trying to leave abusive relationships and the importance of long-term investigative persistence.
If you or someone you know is experiencing domestic violence, resources such as the National Domestic Violence Hotline can provide confidential support.
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