A Mexican national accused of killing four people in Kansas and one in Missouri in 2016 died Tuesday after being found unresponsive in his St. Louis jail cell. Pablo Serrano-Vitorino was found alone in his cell at 2:02 a.m.

He was pronounced dead at a hospital about an hour later, said Koran Addo, spokesman for St. Louis Mayor Lyda Krewson. No further details were released.

Serrano-Vitorino, 43, who was in the U.S. illegally, was accused of fatally shooting four men at a home in Kansas City, Kansas, on the night of March 7, 2016. He was arrested a day later and 170 miles away in Montgomery County, Missouri, where he was accused of killing Randy Nordman of New Florence.

Booking photo of Pablo Serrano-Vitorino Montgomery County Jail via AP

Serrano-Vitorino was charged with first-degree murder in all five deaths. He was being held in St. Louis awaiting an October trial in the Missouri case on a change of venue.

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Missouri prosecutors were seeking the death penalty. Authorities said the shooting spree began when Serrano-Vitorino gunned down his Kansas City neighbor, 41-year-old Michael Capps, and three other men at Capps' home — brothers Austin Harter, 29, and Clint Harter, 27, and 36-year-old Jeremy Waters.

Before dying, one of the victims managed to call police. Authorities have not disclosed a possible motive.

Serrano-Vitorino then allegedly fled in his pickup truck into Missouri. Authorities said he killed Nordman, 49, at Nordman's rural home near Interstate 70, about 70 miles west of St. Louis.

He was captured hiding face-down in a ditch a few miles from Nordman's home, and had a rifle with him, the Missouri State Highway patrol said at the time. A lawsuit filed in Kansas City, Kansas, by the father of one of the victims accused U.S. immigration officials of missing two chances to detain and deport Serrano-Vitorino.

Serrano-Vitorino was deported to Mexico after he was convicted of a felony in 2003 but illegally re-entered the U.S. He was arrested in 2014 and 2015.

After his 2014 arrest in Kansas for battery, Wyandotte County jail officials notified the U.S. Immigration and Customs Enforcement agency he was in custody. But Serrano-Vitorino was released after the agency didn't send an agent to the jail, according to the lawsuit.

Serrano-Vitorino was fingerprinted in Overland Park, Kansas, Municipal Court in September 2015 after he was cited for traffic infractions. ICE officials asked that he be held in custody but sent the paperwork to a different jail in Johnson County, Kansas, the lawsuit contends. Serrano-Vitorino was once again released from custody.

His death comes as President Trump appears determined to use immigration to motivate his base and portray Democrats as soft on security, CBS News chief Washington correspondent Major Garrett reports.

In the process, the president is creating massive unrest inside the Department of Homeland Security with Sunday's resignation of Secretary Kirstjen Nielsen and the departures of Secret Service Director Randolph Alles; the agency's undersecretary of management, Claire Grady; Citizenship and Immigration Services Director L. Francis Cissna; and the department's General Counsel John Mitnick.