Pennsylvania State Police announced 18 charges against a 21-year-old driver accused of striking and killing two state troopers and a pedestrian on Monday, including three counts of third-degree murder, three counts of homicide by vehicle while driving under the influence, and two counts of second-degree manslaughter of a law enforcement officer. 

The two troopers, 29-year-old Branden T. Sisca, 33-year-old Martin F. Mack III, were helping a pedestrian who was walking along the left lane on I-95 South shortly before 1:00 a.m. on Monday when they were struck. 

Both troopers and the pedestrian, 28-year-old Reyes Rivera Oliveras, were killed by the impact. 

Jayana Tanae Webb, 21, was arrested at the scene. She was led out of state police barracks on Tuesday afternoon restrained by handcuffs that belonged to the deceased troopers. 

TWO ALBUQUERQUE POLICE OFFICER AND THREE VICTIMS SHOT, ONE FATALLY; SUSPECT ALSO DECEASED

Shortly before Webb allegedly struck the three individuals, her car was pulled over but officers had to cut the stop short to respond to the pedestrian who was walking on the interstate, Fox 29 Philadelphia reports. It is unclear if Webb was driving when she was initially pulled over. 

Sisca joined the Pennsylvania State Police last year and also served as fire chief of Trappe Fire Company No. 1 in Montgomery County. 

Trooper Martin F. Mack III, 33, and Trooper Branden T. Sisca, 29, were struck and killed in the southbound lanes of I-95 at about 12:40 a.m., Pennsylvania State Police said.

Pennsylvania State Troopers Branden T. Sisca, 29, and R Martin F. Mack, 33, were killed when a driver struck them on Monday morning.  (Pennsylvania State Police)

Martin enlisted in the Pennsylvania State Police in November 2014. 

Both Mack and Sisca were organ donors, allowing them to each potentially save eight lives and help more than 100 others, according to the Gift of Life Donor Program. 

"Heroes in life and death, both were registered organ and tissue donors. Their legacies of helping others lives on through donation," Gift of Life Donor Program President Rick Hasz said in a statement. 

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Pennsylvania Gov. Tom Wolfe ordered flags flown at half-staff called it a "a heartbreaking tragedy that occurred while these troopers were protecting and serving."

"This mournful incident is a stark reminder of the risks—and sacrifices—our law enforcement officers undertake every day to keep us safe," Wolfe said Monday.