The amount of criminal immigrants attempting to enter the U.S. has spiked in recent years, U.S. Customs and Border Protection data reveals.

Over 13,000 "criminal noncitizens" have attempted to enter the U.S. and been apprehended by Border Patrol agents in Fiscal Year 2024, a rise from 4,269 in FY 2019.

CBP defines "criminal noncitizens" as "individuals who have been convicted of one or more crimes, whether in the United States or abroad, prior to interdiction by the U.S. Border Patrol," the agency's website notes.

Such border apprehensions had been on the decline before FY 2021, with CBP recording 8,531 in 2017, 6,698 in 2018, 4,269 in 2019, and 2,438 in 2020. Since then, however, the number has continued to rise, hitting 10,763 in 2021, 12,028 in 2022, and 15,267 in 2023, the most recent full year for which data is available.

ILLEGAL IMMIGRANT SUSPECT ACCUSED OF KILLING JOCELYN NUNGARAY WORE ICE ANKLE MONITOR 

A Border Patrol processes an immigrant

 Immigrants are photographed at a U.S. Border Patrol processing center after they crossed the U.S.-Mexico border on December 07, 2023 in Lukeville, Arizona. (John Moore/Getty Images)

Many of the criminal aliens who have been caught at the border this year have been convicted of serious crimes, including 814 for assault, battery, or domestic violence; 23 for homicide or manslaughter; and 168 for sexual offenses.

But the data does not account for the number of criminal aliens who were able to slip into the country undetected or were released with unclear criminal backgrounds, cases that have once again entered the national spotlight.

Such cases include the arrest of Victor Antonio Martinez Hernandez, a 23-year-old illegal El Salvadorian migrant accused of raping and killing Maryland mother Rachel Morin. Martinez Herhandez had attempted to enter the country illegally four times after being accused of a similar murder in his native El Salvador, the last of which he was able to elude the detection of border security.

In another case, two Venezuelan migrants are accused in the killing of Houston-area 12-year-old Jocelyn Nungaray. In that case, suspects Johan Jose Martinez-Rangel, 22, and Franklin Jose Peña Ramos, 26, entered the country illegally and were released with court dates.

Rachel Morin, left and her alleged killer

Victor Martinez Hernandez is accused of the rape and murder of Rachel Morin August 5, 2023, in Bel Air, Maryland. (Hartford County Sheriff’s Office/Tulsa Police Department)

ILLEGAL IMMIGRANT SUSPECT ACCUSED OF KILLING JOCELYN NUNGARAY WORE ICE ANKLE MONITOR 

While neither suspect had a previous criminal record in Harris County, their background in their native Venezuela is less clear as a result of a lack of cooperation in sharing information between the Venezuelan and U.S. governments.

The two then made their way to what has become an immigrant hotspot in Houston, where Harris County District Attorney Kim Ogg told Fox News has seen an uptick in illegal immigrant crime.

Jocelyn Nungaray murder suspects in separate mug shots

Franklin Jose Peña Ramos, left, and Johan Jose Martinez-Rangel have been charged in the killing of Jocelyn Nungaray in Houston, Texas, on Monday, June 17. (Harris County Jail)

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"Unfortunately, we see a great deal of violence committed by illegal immigrants, and we see as many victimized by other illegals and regular people here. It’s an enormous problem. This was bound to happen," she told Fox News. "It’s one of those things that as an elected prosecutor, you are just waiting for other shoe to drop. I’m just sick and sickened this little girl was the innocent victim of these two monsters."

Get the latest updates on the ongoing border crisis from the Fox News Digital immigration hub.