SAN DIEGO (CNS) - A motorist who rear-ended a vehicle on Interstate 15 near Scripps Poway Parkway, triggering another collision that killed a toddler and her grandmother, was sentenced today to 10 years and four months in prison.

Grant Thoren, 31, pleaded guilty last month to gross vehicular manslaughter and hit-and-run causing injury or death.

Prosecutors were not able to prove that Thoren was under the influence of drugs at the time of the crash, so those allegations were dropped, said Deputy District Attorney Nicole Rooney.

Rooney said Thoren was on probation for drug and theft-related offenses at the time of the accident.

The Vista resident was arrested at his home a few hours after he fled the scene after rear-ending -- and disabling -- a woman's car on southbound Interstate 15 just before 2 a.m. last Sept. 10.

Jasmine Magat's 2-year-old daughter, Keira, and the child's grandmother, 64-year-old Lina Pelembergo Nebrida, were killed when their disabled Honda was subsequently hit by a Toyota Tacoma truck.

Thoren's Cadillac CTS struck Magat's sedan from behind, and the truck hit the Honda before help could arrive, according to the California Highway Patrol.

Jasmine Magat and her 5-year-old daughter were seriously injured but survived the crash. A couple in the Toyota truck were also injured.

Allan Santos, the eldest of Nebrida's nine children, said the entire tragedy has greatly impacted his family.

"My mom was the backbone of our family," Santos said. "It's still a struggle for us."

Santos son said his family has forgiven the defendant, but he still must pay for what he did.

"As a Christian, we do forgive for whatever wrongness, but that doesn't mean that you're free to go," Santos said. "You're going to have to face the consequences. You will be judged by God."

Speaking to the defendant, Santos said, "The bad decision that you made affected all of us."

Nebrida's daughter-in-law, Elaine Santos, told Thoren, "You are the reason they (the victims) are dead."

The Magat family was in the process of moving from Temecula to the National City area when the accident happened, according to their pastor.