MURDERED: Marina Placensia
The day before September 1st, 2016, a woman and her four children boarded a crowded train expecting to arrive in Denver, Colorado for a fresh start. But somehow, overnight, the woman mysteriously dies and not a single person on that train can say how. For seven years, the tragic case of Marina Placensia remained unsolved. Until a relentless detective and a groundbreaking medical re-examination blew the case wide open. Listen now to the inspiring pursuit of justice that was finally able to bring a killer to light.
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Marina Placensia
Courtesy: Chris Medina
Marina Placensia
Courtesy: Chris Medina
Marina Placensia
Courtesy: Facebook
The last photo taken of Marina with her children before they boarded the train to Denver.
Courtesy: Chris Medina
Angelo Mantych
Source: Facebook
Marina with her brother, Chris Medina
Courtesy: Chris Medina
Detective Randy Denison
Courtesy: Randy Denison
File photo of Dr. Bill Smock
Source: Court TV via AP, Pool
Angelo Mantych’s booking photo
Source: Denver District Attorney’s Office
A screengrab from Angelo Mantych’s police interrogation.
Source: Trial Exhibit
A screengrab from the train trip re-creation conducted by investigators in 2023.
Source: Trial Exhibit
Timeline:
Around 7 a.m.
Marina Placensia is estimated to have died aboard the California Zephyr as it approached Denver.
About 20 minutes before arrival
Angelo Mantych says he tries to wake Marina but she is unresponsive. About 10 minutes later, he gets help.
Just before 8 a.m.
Conductors attempt to revive Marina. When the train arrives in Denver, she is dead. Detective Randy Denison notices extensive bruising and begins investigating.
Around 5 a.m.
Denison and a team re-create Marina’s final train ride and determine an assault could have gone unnoticed in the dark train car.
Days later
Dr. William Smock reviews Marina’s injuries and determines she died from suffocation and her death was a homicide.
Denison obtains a first-degree murder warrant for Angelo. That same day, Angelo’s fiancée reports that he strangled and tried to smother her. Angelo is arrested.
Angelo goes on trial and is found guilty of first-degree murder.
Milwaukee, Wisconsin
The California Zephyr train was traveling overnight from Milwaukee to Denver with Marina, her four children and Angelo aboard.
Denver, Colorado
The train's destination and the city where Marina was found unresponsive and pronounced dead.
Episode Source Material
- Original reporting by Sam Anderson.
- Bordelon, Colette. “‘Sis, We Did It’: Brother Believes Justice Was Served Almost a Decade after Sister’s Murder on Amtrak Train.” Denver 7 Colorado News (KMGH), 16 Dec. 2025, www.denver7.com/news/local-news/sis-we-did-it-brother-believes-justice-was-served-almost-a-decade-after-sisters-murder-on-amtrak-train. Accessed 23 Jan. 2026.
- Bradbury, Shelly. “Woman Who Died on Overnight Train to Denver Was Suffocated in Her Seat, Expert Testifies.” The Denver Post, 9 Dec. 2025, www.denverpost.com/2025/12/09/denver-train-murder-suffocation-marina-placensia/. Accessed 23 Jan. 2026.
- Colorado Bureau of Investigation. Identification Record: Angelo Valentino Mantych. Report no. 9389035, Colorado Department of Public Safety, 19 Mar. 2026.
- People v. Mantych. Case no. 2023CR006350, Register of Actions, District Court, Denver County, CO, 16 Jan. 2026.
- People v. Mantych. Case no. 2023CR20012, District Court, Denver County, CO, 30 Oct. 2023.
Resources:
Resources
If you or someone you know is experiencing domestic violence, help is available through the National Domestic Violence Hotline by texting ‘START’ to 88788 or by calling 1-800-799-SAFE (7233).
For state-specific legal information about protection orders, custody, housing protections and more, visit WomensLaw.org.
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