SARASOTA, Fla. (AP) -- A teenager who hurled a hunk of concrete from a highway overpass, killing a University of Alabama professor, was sentenced Friday to life in prison.

Juan Cardenas, 19, was convicted April 27 of second-degree murder.Julie Laible, 32, died instantly when Cardenas tossed a 22-pound rock from an Interstate 75 overpass about 35 miles south of Tampa on March 27, 1999. The block of concrete exploded through the windshield of her car, hitting her in the head.

Prosecutors said Cardenas and three friends were driving around that evening, throwing rocks over overpasses. Jesus Dominguez, 17, who investigators say was driving, still faces trial on a second-degree murder charge.

Noe Ramirez, 16, was convicted in August as a juvenile and served six months of house arrest. Antonio Hernandez Jr., 19, who was standing on the bridge with Cardenas, was granted immunity from prosecution to testify against Cardenas.