2nd student dies after truck mows down group in Oklahoma Six students were struck in the Monday afternoon crash.

A second high schooler has died as a result of a hit-and-run that struck six students near a school in Moore, Oklahoma, officials said Tuesday.

Sophomore Yuridia Martinez died Tuesday from her injuries, officials announced at a news conference. Senior Rachel Freeman died at the scene of the Monday afternoon accident.

The suspect, identified as 57-year-old Max Leroy Townsend, was driving a red pickup truck when he crashed into six students. Townsend did not stop after hitting the students but was apprehended about three blocks away, police said.

Townsend's 29-year-old son was killed Sunday in a car accident, the location of which was close to Monday's scene, according to Moore Police Sgt. Jeremy Lewis. That crash remains under investigation, he said.

Monday's victims were Moore High School cross-country and track athletes, who were running on a sidewalk when they were struck, according to the school district.

Three of the four injured students -- senior Kolby Crum, junior Shiloh Hutchinson and senior Joseph White -- remain hospitalized, officials said Tuesday.

Crum is in critical condition, officials said.

Sophomore Ashton Baza, who suffered a broken leg and broken ankle, was released from the hospital on Monday, officials said.

Before first responders arrived to the scene, "heroic" students jumped in to help their injured classmates, said Robert Romines, superintendent of Moore Public Schools.

"Without hesitation or second thought, our students were there with their friends and began lifesaving tactics including CPR," Romines said at Tuesday's news conference.

Martinez had been thrown from the sidewalk to a pond and several students jumped in the water to get her, Romines told ABC News.

And when classmates went to help Crum -- who is in critical condition Tuesday -- Crum told them, "Go to the next one, I’m OK," Romines said.

"That’s a true testament of what we've got over at Moore High School," Romines said. "Just very proud of our students."

Townsend was arrested Monday for first-degree manslaughter and multiple counts of leaving the scene of an injury accident.

"There were signs of impairment" based on a field sobriety test, Moore Chief of Police Todd Strickland said Tuesday.

Townsend has an "extensive criminal history" involving DUIs and leaving the scene of an accident, said Sgt. Lewis.

A motive for the deadly crash is not known.

"We will find out why," Lewis vowed.

In the wake of the "unthinkable tragedy," 30 mental health specialists are being brought in to work with students and staff, Romines said.

A vigil will be held Tuesday evening at the high school, Romines said.

ABC News' Victor Oquendo, Gina Sunseri, Marilyn Heck and William Mansell contributed to this report.